From Halopedia, the Halo wiki
General Howard Graves was a human rebel, one of three people who made up the leadership of the United Rebel Front. As a member of the rebel leadership, Graves was a valuable target that the UNSC would have loved to capture.
Operation: SMOKING ACES
The Insurrectionists were dealt a series of blows in 2531 when the SPARTAN-IIs sabotaged a number of their operations. This attracted the attention of Graves, who began to target the Spartans directly. In May 2531, he planned an elaborate ambush for them at Camp New Hope using several FENRIS nuclear warheads and an antigravity plate.
During the course of the ambush, he underestimated the Spartans, and was killed while trying to spring the trap after an Asteroidea anti-personnel mine thrown by SPARTAN-051 exploded and sent a piece of shrapnel into his skull. John-117 described the loss of Graves as "unfortunate," as he held the secrets that ONI would have desperately wanted to get their hands on as well as knowledge of how far the rebels had penetrated within the UNSC.
List of appearances