Hammersmith was a male Human Starfleet officer in the 23rd century. As of 2269, he had earned the rank of Vice admiral, and was assigned as commanding officer of Starbase 29. He was a powerfully-built, dark-skinned man, with a strong belief in Starfleet and his purpose as an officer.
In 2269, Hammersmith was the senior officer overseeing operations at Talin IV, following the disaster on that world, and the abandonment of the First Contact Office outpost on Talin's moon. As such, brought the initial charges against the USS Enterprise officers -- James T. Kirk, Spock, Hikaru Sulu, Nyota Uhura, and Pavel Chekov -- deemed responsible for violating the Prime Directive and causing the Talin disaster and the loss of the Enterprise. When Kirk resigned his commission, Starfleet opted not to hold courts martial for the other four officers. Leonard McCoy, angered that there was not to be a formal proceeding, and that he was being transferred back to San Francisco, punched Hammersmith before witnesses, then resigned before assault charges could be brought.
In the months that followed, Lieutenant Commander Montgomery Scott, still serving as chief engineer during the efforts to restore the Enterprise, attempted to tender his resignation to Hammersmith. The admiral refused to accept it, but did offer to allow Scott to go over the head of the ship's temporary commander, Lieutenant Lawrence Styles, and gather evidence that the damage to the Enterprise had come from a source other than a Talin nuclear weapon.
Later, after Spock and the other former Enterprise officers had discovered the unknown alien creatures actually responsible for Talin's nuclear war, Hammersmith authorized Scott to take the Enterprise and further investigate, angering Styles to the point of insubordination. (TOS novel: Prime Directive)