An accident leaves only me and my spherical friend
Tom Hanks as Chuck Noland in "Castaway"
I'm quite the hubristic tricky trickster
Tom Hiddleston as Loki in "Thor"
I break backs and grew up in gloom
Tom Hardy as Bane in Batman: The Dark Knight Rises
I'm a pompous member of the snake crew
Tom Felton as Draco Malfoy in the Harry Potter movies
I die a lot to save the world from E.T.s
(original answerer's answer)Tom Baker as The Fourth Doctor in Dr. Who
(question poster's intended answer)Tom Cruise as Cage in Edge of Tomorrow
I'm an agent in darkness, but you probably don't remember meeting me
Tommy Lee Jones as Agent K in Men In Black
Your name is