Glad Hand (Sean Young) was one of only four adults featured prominently in West Side Story (the other three being Sergeant Krupke, Lieutenant Schrank and Doc), but is the most minor of the four, as his character appeared only in the gym dance scene.
Glad Hand is a social worker. He is perpetually cheerful and has a bombastic air of welcome and makes repeated attempts to prevent trouble, but these don't always work as he wants.
John Astin, who played Glad Hand (but was uncredited in the film), later became better known for his iconic role as Gomez Addams in The Addams Family TV series (1964-66). He is also known for replacing Frank Gorshin as the Riddler in two episodes of Batman (1966-68), and later still for his recurring role as Buddy Ryan on Night Court.