Lieutenant Commander Calvin “Cal” Hudson was Starfleet’s first attaché to the Federation colonies in the Demilitarized Zone. He grew sympathetic to their cause, and in 2370, joined the Maquis (DS9 episodes, “The Maquis, Part I” and “The Maquis, Part II”). Even his former long-time friend Benjamin Sisko could not dissuade him from abandoning his duty to Starfleet.
Hudson escaped capture, and became a great leader among the Maquis. We heard about his death fighting the Cardassians in 2373 from Michael Eddington in the episode “Blaze of Glory”. But then again, Eddington has been known to lie. A lot. So, Cal Hudson could still be very much alive.