Sinew was a member of the second Omega Flight, which was founded by the Master to serve as his superhuman operatives. Sinew was feral both in appearance and nature. He possessed not only an animal's appearance but an animal's senses and he seemed to be able to detect evil.
Omega Flight was later used by the Master against Alpha Flight after he had tired Alpha Flight out by manipulating them into facing the Hardliners. During the battle, the Master of the World grew frustrated and attempted to kill both Alpha and Omega Flight but his effort was disrupted when Sasquatch threw Sinew at him. This disruption allowed Alpha Flight to rally for a period and defeat Omega Flight and, eventually, the Master. Omega Flight, defeated, seemed to disband. Some of its members have been seen since but most have remained either in hiding or in prison.
Powers and Abilities
Sinew is an animalistic creature (he is covered in fur, has claws, a tail and a less developed posture than most humans) with enhanced physical abilities and senses.
His real name was revealed in the Official Handbook of the Marvel Universe A to Z Hardcover Vol. 7