Captian Wallace
From Halopedia, the Halo wiki
Captain Wallace was a UNSC officer. In 2525, he was captain of the UNSC Commonwealth. Wallace lost his left arm below the elbow some time in his career. Rather than utilize an artificial limb, he simply did not have a left arm, something that probably took getting used to by his crew.
Although an exceptionally brilliant tactical officer, Wallace was rather by-the-book and did not enjoy having civilians on his bridge, as evident by his displeasure of Dr. Catherine Halsey.
Wallace and his ship was instrumental in helping the Spartans cripple a Covenant frigate sufficiently enough for them to destroy it.