Number Two (real name unknown) was an Earthforce Marine Corps officer, veteran of the Earth-Minbari War and Mars Resistance leader.
During the Earth-Minbari War, this man became familiar with denn'boks when he took one off a dead Minbari.
In the Earth Alliance Civil War, this man became part of the Resistance and became the second-in-command, taking the codename Number Two. He went to rendezvous with two people from Babylon 5 on Mars, but couldn't know who. He met Stephen Franklin and Marcus Cole with Captain Jack, but held them until he could verify their identities. He found they didn't match, but that was due to Jack switching the IDs. Number One came in the room when he confronted them and they found out the truth.[1]