Admiral Nimembeh was a Starfleet flag officer serving at Starfleet Command during the mid-24th century. During his career, Nimembeh had also taught the course called Tactical Analysis at Starfleet Academy.
Chakotay gave his resignation to Admiral Nimembeh on March 3, 2368 before joining the Maquis. Seven years later, Chakotay said he could still remember "the look on the Admiral's face." (VOY: "In the Flesh")