From Sonic Retro
The G.U.N. Commander (known as Shirei-kan (司令官) in Japan and called Abraham Tower in the Archie comics series) is the highest-ranked leader of the Guardian Units of Nations, the prominent military organization of Sonic's world. The Commander saw his debut and most major role in Shadow the Hedgehog, where he was in charge of the effort to repel the Black Arms invasion of the planet.
The game's manual describes him as a man "with complete confidence and an iron will... totally unshaken even as the Black Arms attacks". In addition to commanding military forces during the war, the Commander orchestrated the evacuation of Central City's civilian population, and ensured that the United Federation President was conveyed safely to the GUN Fortress via Air Fleet. He also appeared briefly in Sonic Chronicles: The Dark Brotherhood, co-ordinating G.U.N.'s efforts to track the Marauders' movements through satellite reconnaissance.
The G.U.N. Commander is roughly sixty years old, and sports a short grey crew cut. The Commander's most striking feature is his heterochromia iridum - differently coloured eyes, one cyan and one orange. He is always seen wearing his grey general's uniform, and a similar pair of white gloves to Eggman or Sonic.
During most storylines in Shadow the Hedgehog, the Commander is shown as being unrelentingly hostile to Shadow, ordering his soldiers to shoot the hedgehog on sight even in the face of overwhelming evidence that Shadow is on their side. It's later revealed in a flashback why the general persists in this attitude: he spied into Professor Gerald Robotnik's lab during Shadow's creation, witnessing Black Doom's unnerving participation in the hedgehog's genesis. On top of this, the young Commander blamed Shadow for Maria's death, as the whole reason that G.U.N. of 50 years ago assaulted the space station was to shut down Gerald's research on the Ultimate Lifeform. The Commander even makes personal attempts on Shadow's life on some routes through the game; using his trademark pistol on the ruined ARK, and again inside the Diablon mech in some of the Stage 6 boss battles.
During the Last Story, however, the Commander seems to forgive Shadow, or at least accept that Maria's death wasn't his fault. In Extra Mode, he sheepishly makes efforts to excuse his behaviour by mentioning that he'd recently become a grandfather.
The Commander is voiced by Marc Thompson in the English version.