Pyerpoint was a High Archon on the Rock of Judgement. Secretly, he used his connections to become the head of a large criminal empire. When acting in that capacity, he sometimes used the alias "Sentinel".
When Xais was alive, they were allies. She promised Pyerpoint to use her psychic powers to imprint his brain patterns in helicon, making him immortal. In fact, she planned to double-cross him in her campaign to kill all "Normals". After Charlie Nisbett killed the body Xais was controlling through her helicon death-mask, Pyerpoint took the mask and fled. Romana II chased him, and he forced the mask onto her.
Later, when Romana freed herself, Xais convinced Pyerpoint she still could store his mind in helicon and had him put on her mask. While struggling for control, he was killed by one of the station's robots, which Pyerpoint had ironically programmed earlier to kill any intruders. (PROSE: The Romance of Crime, AUDIO: The Romance of Crime)