Agent J

James Edwards chases a suspect who isn't human and impresses Agent K. He passes the MIB tests, erases his old life and becomes J. With K, he investigates the death of an Arquillian prince and learns the galaxy is on a cat's collar. In the end he neuralyzes K, who retires, and carries on with medical examiner Laurel, now Agent L.

Five years later, J is one of the best agents, but he neuralyzes partners who can't handle the work. He breaks protocol by not neuralyzing Laura, a witness. To find the Light of Zartha, he brings K back from the post office where he works, stops by pawnbroker Jack Jeebs and faces the villain Serleena. In the end he loses Laura and is shaken.

In 2012, K vanishes from the present, and only J remembers him. He travels to 1969, is arrested by a younger K and convinces him of his mission. With Griffin and a visit to Andy Warhol's Factory, he goes after Boris. J has to tell K that he will die, and ends up discovering a fact of his own past tied to that day.

Will Smith was cast, per Wikipedia, partly because director Barry Sonnenfeld's wife was a fan of The Fresh Prince of Bel-Air. The studio and Spielberg preferred Chris O'Donnell. In the animated series, J is voiced by Keith Diamond.