Colonel Robert Watts
From Halopedia, the Halo wiki
Summary
Formerly a member of the UNSC, Colonel Watts became a turncoat and a traitor some time before 2525, abandoning the military and joining the Eridanus Rebels. He eventually became the leader of the rebels and governor of the rebel stronghold of Eridanus Secundus. In 2525, he was captured by a team of Spartans and brought back to ONI for interrogation.