Marie Lathrop was the daughter of rancher Jim Lathrop during the days of the American Frontier. She lived on her fathers ranch with her brother Bobby. They lived on a ranch in the town of Leadville, Texas. They were soon terrorized by the Eastern Syndicate led by Blast Barrows, who was forcing ranchers off their land. However Barrows was smitten by Marie and asked her to marry him but she refused. To pressure her he shot her boyfriend and ranch hand Charlie. Marie and her father Jim then rushed Charlie to the local doctor Matthew Masters who, unknown to them, promised years ago to the Governor of Texas to never kill again and took up medicine instead. When Barrows returned and killed Charlie and Jim stormed off to stop him, Marie called Masters a coward for not willing to fight. This opinion intensified when Jim was shot and injured by Barrows as well. Marie's stinging words prompted Matthew to create the masked identity of the Black Rider after he learned that Barrows and his gang intended to burn the Lathrop ranch to the ground.
Lathrop and his gang attacked the ranch, but were ambushed by the Black Rider. As his gang was being shot down around him, Blast Barrows managed to nab Marie and ride off with her. The Black Rider caught up, knocking both Barrows and Marie off the horse, then killed Blast in a duel. Marie was instantly smitten by the Black Rider who told her to be tolerant of Matthew Masters as he was a good doctor. Marie indeed tolerated Masters, but still considered him a coward and refused his request to court her. Masters instead began romancing Marie as the Black Rider.
Master perpetuated his double identity even though it meant that Marie constantly scorned Matthew Masters, and pined after his alter-ego. More often than not, Marie often found herself being rescued by the hero by one danger or another.
While taking care of her nephew Bobby, Marie was at the local general store when the town was under siege by Killer Kane and his gang. When Bobby was struck by a bullet she rushed to Matthew Masters for medical aid. While she scorned Masters for ducking out after Bobby was treated, she was elated when the Black Rider arrived to clear Killer Kane and his boys out of town. Marie joined Matthew Masters in recovering a government agent whose coach was crashed in a botched attempt to steal all his silent contract bids for a government irrigation contract, berating Masters' lack of courage the whole way. Later when Marie was kidnapped by Ben Jonas and his gang, she was rescued by the Black Rider, whom she thanked with a kiss. During the Black Rider's battle with Snake Bostwick, who sought to force the Lathrop's from their property, Marie's brother Bobby learned the Black Rider's secret identity. Sworn to secrecy, Bobby teased his sister about her opinions regarding Masters and the Black Rider, suggesting that the hero of her dreams might be closer to her than he though. Marie was too oblivious in her lovelorn state to take the hint. In the middle of an escalating feud between Leadville ranchers and the nearby nesters, Marie was disheartened to learn that the Black Rider had paired up with outlaw Red John, until the hero exposed that John was posing as the Black Rider, clearing his name.
When a local named Waller was pressuring Marie and the other locals of Leadville to vote for him as sheriff. This was stopped by the Black Rider who uncovered that Waller owned all the mortgages on the local ranches and was seeking the position to impose a tax on ranchers cattle in order to make them too cash strapped to pay their mortgages and be evicted. With the mortgages transferred to Snake Barstow, Snake attempted to force the ranchers off their land by ordering them to pay up. Snake then pressured Marie to marry him in order to safe her father's ranch. However, this plot was foiled when the Masked Rider and the Phantom slew Barstow and his gang. Soon, the horses on the Lathrop ranch were being stolen by Bush Bennette and his gang, who also kidnapped Marie in the process until she was once more rescued by the Black Rider.
Marie was kidnapped in three succeeding instances shortly thereafter. First she was used as a hostage by Tod Sultan who was posing as the Black Rider until he was slain by the real hero. While riding around Mystery Mountain, Marie was kidnapped by a long list tribe of cavemen to be sacrificed, until she was rescued by the Black Rider. Lastly, Marie attracted the attention of the Hypnotist who sought to use his hypnotic powers to take over the United States. He hypnotized Marie, intending her to be his new queen, but like with the others the Hypnotist was stopped by the Black Rider.
Shortly thereafter, Marie began to be romanced by Bostonian scientist Professor Chalis who had come to the region to conduct human growth experiments. Driven mad by exposure to his his own device, he captured both Marie and the Black Rider in order to subject them to his experiment, but the Black Rider managed to free them both, slaying Chalis in the process. After the Chalis incident, Marie was once again romanced by a wealthy visitor -- this time a railroad politico named Mr. Cantrell. Unknown to her, Cantrell was inciting a war between a local tribe of Native Americans to force area ranchers to sell their property cheap. Marie was caught in the crossfire when her fathers ranch was attacked. Marie was horrified when her brother Bobby was wounded by an arrow. However the quick acting Dr. Matthew Masters treated Bobby, earning a new respect from Marie. Cantrell was soon exposed by the Black Rider and brought to justice. Marie's warming toward Masters was quickly strained again after she became jealous at Masters when he treated another woman named Belle Raven who afterwards was exposed by the Black Rider to be the outlaw known as the Fox. Still, she was committed to making a "real man" out of Masters, and invited him to the Leadville rodeo where the Black Rider was scheduled to put on a show, hoping the spectacle would teach Matthew how to be more brave. Masters however quickly earned her ire by making an excuse to slip away so he could change into the Black Rider. The town was soon taken over by another outlaw calling himself the Fox who sought to make a reputation for himself by luring the Black Rider into a trap and killing him. He took Marie hostage while the Rider was out of town, however the Black Rider managed to see through the trap and gun down the Fox, saving Marie's life once more.
When the Lathrop ranch was terrorized by a puma, Marie stubbornly went out to stop it on her own despite warning of the danger involved. Confronted with the puma, Marie was horrified to find that her gun had jammed. However the Black Rider, as always, came to her rescue and the puma was trampled to death by his horse Satan. When Flush Dawson opened a new casino in Leadville, Marie brought Matthew Masters along with her. However, Masters was soon bilked of his money at the crooked games and tossed out while Flush Dawson made a romantic pass at Marie. However, like Marie's prior suitors, the Black Rider exposed Flush Dawson as a fraud and gunned him down. Not long after Marie was one more jeopardized due to her association with the Black Rider when Smoke and his Border Riders came to town seeking to eliminate the hero. They kidnapped both Marie and Matthew Masters and kept them hostage. They were both rescued by Marie's brother Bobby, who briefly posed as the Black Rider to free Masters so he could deal with Smoke and his gang. The Black Rider took Marie to a Leadville dance shortly thereafter where he had a close call wherein his identity was almost exposed. When Marie's cousin Oscar Tippitt came to Leadville from Boston, she helped him get a job at the local bank. However the bank was robbed, by Oscar and some outlaws and Tippitt was brought to justice by the unlikely Matthew Masters. Marie was once again put in danger when her and her father were captured by the Native American warrior Wolf Claw who sought to start a war between his tribe and the people of Leadville. As usual, the Black Rider came to Marie's aid and freed her. Later, Marie was jealous when both Doc Masters and the Black Rider Miss Van Ryn, who traveled from St. Louis to claim her family mine.
Soon afterward, Doc Masters left Leadville to become a frontier doctor for a time. Marie's subsequent activities during his absence are unrecorded. However during that time she did not seem to realize that Masters and the Black Rider were the same man, even when both were absent at the same time. When both Masters and his alter-ego returned to Leadville, Marie still carried a torch for the Black Rider, however her romantic interests for Masters had cooled some. Still, with the Black Rider back in town, Marie soon found herself getting into plenty of trouble necessitating the Black Rider coming to her rescue. The earliest of these included the Black Rider impostor Hatchet Haines and stage coach robber Lola Montace. When the town of Leadville was terrorized by outlaw Whip Wade, Marie was in direct danger and saved by the Black Rider once again. Shortly thereafter when her brother Bobby went missing, Marie went to Matthew Masters to help look her him. The pair were kidnapped by outlaw Tip Tomlin who had kidnapped Bobby to force the secret identity out of the boy, but had beat him into a coma. Taken to Tomlin's hideout, both Matthew and Marie treated Bobby who came out of his coma. Bobby then promised to reveal the Black Rider's secret, but only if Matthew left the room. This allowed Masters to change into the Black Rider and slay Tomlin and his gang. The Black Rider then fled and quickly changed back into his alter-ego, apparently leaving Marie none the wiser that the two men were one and the same. Later Marie assisted Matthew Masters and her father help treat a plague stricken Comanche tribe. When another Native American, this one tortured and having had his tongue cut out, ended up under the care of Matthew Masters, Marie was called to help perform surgery on the man. Later, Marie was captured by the men who beat the warrior. Marie was taken to the mine where the outlaws had enslaved a number of Native Americans until she was rescued by the Black Rider again. Marie also assisted Masters as a nurse when outlaw Bull Barnes forced Masters to perform surgery on him to remove a bullet put in him by the Black Rider, later the hero slew Barnes.
When Marie's father fell ill, she assisted Matthew Masters once again in performing medical aid. Moments later, the Lathrop ranch was visited by Blackie Thorp and his gang who demanded fresh horses to escape the law. Marie refused and asked Matthew to stand up to the outlaws. However Matthew's vow of nonviolence prevented him from doing anything, angering Marie when Thorp shot Bobby and fled with the horses he wanted. After Matthew treated Bobby's superficial wounds, he went after the gang as the Black Rider, getting revenge. Later, the Black Rider met with Marie and told her not to be so harsh toward Matthew Masters as he helps people in his own way.
When Dr. Stevens came to town to set up a rival medical practice, Marie instantly became smitten by him when Stevens showed that he was more aggressive and willing to stand up for himself unlike the meek Matthew Masters. However, unknown to Marie Stevens was a fraud who was the leader of a gang of outlaws. When the outlaws shot Bobby, she took him to see Dr. Stevens who did a hatchet job while trying to pull the bullet from Bobby's leg. Realizing that Stevens lacked the skill needed to treat Bobby, Marie tearfully brought him to Matthew Masters who removed the bullet from Bobby's leg. Later as the Black Rider, Masters exposed Stevens for the fraud that he was.
When Marie's father Jim was a star witness in a trial against Curly Adams, Adams had his gang kidnap Marie and her brother Bobby. The pair were eventually rescued by the Black Rider and Jim's testimony saw Adam's punished for his crimes. Not long after, Marie and Bobby left Leadville on a trip along the Golden Express Railroad. Unknown to the pair at the time, the Black Rider prevented Jack Grimes from blowing up a rail bridge the train crosses, saving their lives. Later, Marie became the object of affection for outlaw Stinger Ray, who kidnapped both Marie and Bobby in order to force her father to consent to Stinger marrying his daughter. As with other kidnap attempts, this one failed thanks to the intervention of the Black Rider. Marie was later among the citizens of Leadville who were terrorized by both the seemingly undying outlaw known as the Spider, as well as the Lobo gang and their pack of trained wolves, in both instances Marie was protected by the Black Rider.
Marie soon started taking up a role as a part time nurse for Dr. Matthew Masters. Such as when Matthew was caring for the son of Sheriff Ben Yarby, who had fallen ill. Not long after this, Marie and her father also assisted Dr. Masters in treating a tribe of Comanches who had contracted Cholera. While treating the Comanches, Marie began to notice similarities between the Black Rider and Matthew Masters, but apparently did not come to the realization that they are both the same man. When her father began losing stock and became desperate to win fast money to save his business, Marie warned Matthew Masters that he entered a poker game with crooked gambler Luke Halsey, leading to the Black Rider intervening and preventing Jim from losing his livelihood on the card table.
When escaped con Slasher Slade made a connection between the Black Rider and Matthew Masters, he kidnapped both Marie and Matthew in order to learn the secret identity of the masked hero. Masters convinced Slasher to let him go so he could bring the Black Rider to the outlaw and his gang and quickly changed into the Black Rider and freed Marie. Shortly thereafter Marie and her family were held hostage by Spur Cameron who was wounded clashing with the Lathrop ranch hands while trying to rustle their cattle. However, the family was rescued not by the Black Rider, but his alter-ego Dr. Matthew Masters who had his medical license revoked when the star witness in the trial against Cameron died under mysterious circumstances in which he could not solve. Masters forced a confession for the witnesses murder in exchange for medical treatment and quickly disarmed Cameron, and put him into custody, freeing the Lathrop family and regaining his license to practice in the process.
During the Black Rider's time in Leadville, Marie apparently did not divine that he and Matthew Masters were the same man.