Charter members of the Outsiders, 1971

Dr. Fate
Aquaman
Martian Manhunter
Blockbuster
—joined later by Power Girl

Bit of a cheat here, as only one of the above DC characters were ever in the Outsiders, which was conceived as a team for Batman to lead, whereas the Defenders were a “throw these dudes with not much common purpose together and call it a ‘non-team’" thang. But both teams have often been highly mutable, so this’ll do.