Onaaka Matrin was the Commander of the Second Tulkan War Fleet and a member of the Tulkan War Council who had their memories erased after being defeated by the Annarene.
In 1979, Sooal hijacked the ship the Council was on as it was enroute to a penal world, and brought it to Earth to restore their memories. It took three years to accomplish this, during which time he was a resident at Graystairs with the name Eddie. The Seventh Doctor enabled him to remember his past life, and he joined his fellow Tulk. After getting Onaaka Matrin's part of the access code to open the Council's weapons stasis chamber, Sooal killed him. (PROSE: Relative Dementias)