Sadan Rassul was the high priest of Horus in ancient Egypt, then of Nephthys. When the Osirans defeated Sutekh and Nephthys, her imprisonment was to have her mind split. Her reasoning was sealed in a canopic jar, while her instincts were placed in the mind of Rassul's daughter. She was mummified, and Rassul was granted immortality so he could eternally guard the tomb. However, the canopic jar was cracked during a tomb raid, and Nephthys was able to influence Rassul.
When Kenilworth's expedition found the tomb, he allowed them to take the comatose Nyssa back to England. However, he did not want some of the artefacts to leave. He reanimated Nicholas Simons' corpse and used it and some Osiran service robots to try to prevent this. In England, he kidnapped an earlier version of Nyssa and used an Osiran lodestone to send her back to ancient Egypt, to be the receptacle for Nephthys mind. Once Nephthys died, Rassul's immortality ended and he disintegrated. (PROSE: The Sands of Time)