Colonel Grimm (also known by his nickname, Happy Jack) is the commanding officer of Bravo Company, and thusly Sergant Hawk's direct commanding officer. Col. Grimm also has a daughter named Vikki Grimm.

He first appears in Army Men: Sarge's Heroes and would continue to appear in the games featuring Sarge (Hawk), including Army Men: Sarge's Heroes 2, Army Men: Turf Wars, Portal Runner, Army Men: RTS, and the dubiously canon Army Men: Sarge's War.

Despite only being a colonel, Grimm seems to be the highest-ranking military officer in the Green Army in the games he appears in. Grimm is entrusted with attending Field Marshal Tannenburg's surrender on behalf of the Green Nation. 

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