Leo Zelinsky first appeared in The Amazing Spider-Man #502, and was created by J. Michael Straczynski and John Romita Jr.
Leo Zelinsky was a simple tailor who owned a small shop in a bad neighborhood of New York City. Then, one fateful day, the Thing came in looking for a new costume after losing all his clothes in a fight. Zelinsky designed and made Ben Grimm a new uniform on the spot, impressing the crime-fighter with the quality and speed of his work. Through word of mouth, Zelinsky became a huge hit with the superhuman crowd.
Zelinsky has made costumes for superheroes--such as members of the Avengers and the X-Men--as well as for villains--like Doctor Doom. To avoid confrontation between the heroic and villainous extremes of his clientèle, Leo divides his schedule between heroes and villains. On Monday, Wednesday, and Saturday Zelinsky works for his hero clients; on Tuesday and Thursday he does work for villains.
Leo also maintains a strict confidentiality policy for all of his clients, protecting their identities while he works on their attire. However, Zelinsky once broke this policy when he revealed information about the villain Killshot to Spider-Man in order to prevent a murder. Spider-Man prevented the crime but the masked villain escaped.
Killshot did come after Leo Zelinsky to exact revenge but Spider-Man saved the tailor's life and saw that Killshot was sent to jail. Later, Leo offered to make Spider-Man a costume at a steep discount as thanks. What Leo didn't realize was that the design of the costume he was offering to Spider-Man was the same that Parker had seen himself wearing in a vision of the future during a tragic last stand as a hero. This dulled any enthusiasm Parker would have otherwise had for the gift.
Leo also designed Robbie Baldwin's costume for his Penance persona, a job that was notable for how disturbing the design was. Mired in guilt over the events that destroyed the town of Stamford, Baldwin had insisted that spikes be embedded on the interior of the costume, causing constant pain to the wearer. Leo was especially agitated when Baldwin asked for his help to put on the torturous costume.