Grumman

Lieutenant General Grumman is Colonel Roy Mustang's commanding officer and mentor at East City headquarters. He plays chess with Roy Mustang when the transfer to central has came for Roy, Roy then bests the Lieutenant General in a game of chess to which the General gives him the board (And pieces) as a farewell gift. He is an old man that takes a lighthearted approach to his command. When Roy Mustang transfers from Eastern Headquarters to Central, Grumman authorizes the transfer of Mustang's subordinates, including his granddaughter Riza Hawkeye (though it is unknown if she is aware of this relationship). He makes no further contributions in the anime, though during a brief cameo in Conqueror of Shamballa he is implied to have replaced King Bradley. In the manga, after the homunculi strip Mustang of his subordinates, he calls for Grumman's aid. Grumman, not under the homunculi's surveillance, has since been acting on Mustang's behalf in intelligence gathering and communication. Though a willing ally, he is reluctant to openly work against the military as becoming a traitor would make it difficult to become the leader of Amestris. It is implied in a joke that Grumman doesn't do anything in the East City Headquaters when he says to Roy: "Now that your transfer to central has become final, I may have to start doing things around here again.", although this may just be an inside joke between the two.

Trivia

 * The kinship between Grumman and Lt. Hawkeye (Riza) is not declared at any point during the course of the manga, but it is stated at the Perfect Guidebook 2. The book reveals he's her grandfather on her mother's side (and therefore, don't bear the same surname). It's unclear whether Riza is aware of this kinship, since she states she doesn't know about any relatives (to Mustang, in Chapter 60 of the manga), but he's aware, as he even suggests Mustang to 'marry his granddaughter', so she would become the Fürher's wife.
 * Like nearly all military personnel in the Fullmetal Alchemist series, Gel. Grumman is named after a military vehicle, vessel or weapon, in her case, the Grumman E-2 Hawkeye, an aircraft carrier-based tactical Airborne Early Warning (AEW) aircraft used in the US Navy. Interesting enough, his granddaughter's name was also took from the same aircraft.