Solis was a Time Lord. He was a member of the Chancellery Guard and was one of Chancellor Goth's personal bodyguards.
The Decayed Master hypnotised Solis and commanded him to kill the Fourth Doctor by disconnecting him from the Matrix whilst he was still connected to it. Solis presented himself to Castellan Spandrell and Coordinator Engin, saying that the Chancellor wanted the Doctor brought to him. Carrying out his orders, he attempted to reach for the disconnection control, something he tried several times before being shot with a staser by Spandrell. (TV: The Deadly Assassin)
Solis did not immediately die and Engin was forced to shoot him multiple times until he did so. (PROSE: Doctor Who and the Deadly Assassin)