Bill Filer

Bill Filer was an American agent sent to discuss the threat of the Master with UNIT.

Biography
Being shut out of the rest of the proceedings by Chinn, Bill left, intending to return to his base of operations. On his way back he passed by Axos. Intending to investigate, he was captured by the ship, scanned, duplicated and held prisoner alongside the Master.

His shouts for help were heard by Jo when she and the Third Doctor visited the ship and got lost inside it. With the Master's help, he escaped by shooting a nerve centre. He arrived at the complex just in time to help destroy the duplicate of himself. For the remainder of the crisis, he helped the Doctor and UNIT defeat the Axons and the Master and was witness to the Nuton Power Complex explosion. (DW: The Claws of Axos)