He and his wife, Ruby Dee were involved in organizing the 1963 March on Washington.
Grumpy Old Men (1993) [Chuck]: Dies (off-screen) of a heart attack. (Thanks to Michael)
Get on the Bus (1996) [Jeremiah]: Dies of a heart attack on the bus. (Thanks to Michael)
Bubba Ho-Tep (2002) [John F. 'Jack' Kennedy]: Killed by the mummy (Bob Ivy). (Thanks to Val)
Night Gallery (1969 TV) [Osmond Portifoy]: Presumably killed (off-screen) by Roddy McDowall after Roddy comes back from the dead; the story ends with Ossie reacting in terror to the changing painting showing Roddy emerging from the grave, but the implication of his fate is pretty clear. (Thanks to Michael)