was a Federation Starfleet flag officer
on active duty in at least the mid-23rd century
In the 2260s, Admiral Leslie was assigned to the Starfleet Operations division. He had at least one son, also serving in Starfleet. (Star Trek: New Voyages: "Come What May")
In an alternate continuity, his given name was Edward and he was chief engineer of the SS Yorktown in the late 2220s.