Longshot started his life in a 1985 six-issue limited series from Marvel Comics, written by Ann Nocenti and pencilled by the legendary Art Adams. This limited series was a self-contained story, not counting the cameos by Spider-Man and She-Hulk and the significant guest appearnce by Dr. Strange. The character proved popular enough that Longshot was added to the X-Men lineup very shortly after, through a convoluted plot device that wiped out all of his memories from the limited series.
Longshot originated from an alternate dimension ruled by a bloated cyborg named Mojo, where video programming was king and Longshot was the most successful actor/stuntman of them all. Like the other actors, though, he was a slave to Mojo, forced to perform in real battles for entertainment. His world was populated with flying backpacks, laser guns, floating camera ships, and other assorted high-tech frippanry. It was something like "Gladiator" crossed with "Survivor" using "Titan AE" technology.
The main reason Longshot was so successful, it turns out, was that he was genetically engineered with phenomenal luck. His luck manifested as a glowing left eye and only worked on the condition his motives were pure -- he could throw a blade at an attacking villain and expect it to hit him right in his weakest spot, but expecting to make a fortune in gambling just wouldn't happen.
Aside from this, Longshot had hollow bones, making him light enough to perform truly phenomenal acrobatics, and three fingers and a thumb on each hand. His weapons of choice were short throwing blades he kept in a bandolier. Oh, and he was extremely good-looking, or at least all the characters around him said so. It must have been the long blonde hair. (This is what happens when you let women write the comics for a change.)