Thirty eight year old Major Henry Ellington was the lead engineer aboard the Cerus-subclass battlestar Cerus before the start of the Second Cylon War. After a series of events resulting in Stacey Moore's reassignment to another ship, Admiral Nikitas made the engineering officer the executive officer aboard Cerus.
After the destruction of Cerus, Ellington is promoted to Lieutenant Colonel and is placed as the executive officer of the Olduvai-subclass battlestar Atromitos, serving as Admiral Nikitas' right hand man.