Professor Sico Rudo was a Imperial Japanese scientist who was active during World War II. By the summer of 1945, he developed a weapon for the Japanese he called "Atom Water", a liquid that when evaporated caused a powerful explosion. To test it out, he and a group of Japanese soldiers used it on a Japanese island that recently was captured by the Americans, with each sample going off in areas that the military were clearing.
The blasts prompted Captain America and Bucky to investigate it further. Following the trail of explosions to the cave where Rudo and his men were hiding out, Cap and Bucky were captured. Rudo then left them tied up in the sun surrounded by Atom Water and left a sample vial behind to mock them while they went to cause more destruction. Breaking free, Cap tossed the sample vial into Rudo's cave. Tracking down Rudo and his men, Cap and Bucky attacked. With his men losing the battle, Rudo shot his own men and fled back to his cave. When Cap and Bucky failed to follow them, he accused them of being cowards just moments before the broken vial of Atom Water exploded, killing him instantly.
Recovering a sample of Atom Water from one of the dead soldiers, Cap turned it over to the military where he was informed America had developed a more powerful weapon: The Atom Bomb.
Rudo was armed with a pistol. He also invented "Atom Water", a highly explosive liquid that would explode when evaporated by the sun.