An ingratiating comedian and actor with a knack for impersonations and musical parodies, Jimmy Fallon brought boyish energy to the venerable sketch comedy series “Saturday Night Live” (NBC, 1975- ) between 1998 and 2004. His tenure on the show, which included a sublime pairing with head writer Tina Fey on “Weekend Update,” led to several high profile television stints, including host of the MTV Movie Awards in 2005, and appearances in feature films like “Almost Famous” (2000) and “Fever Pitch.” (2005). His movie career never quite panned out, and Fallon kept a low profile until 2008, when he