Hassan the Undying was a person (possibly Orion) in the 24th century and member of the Orion Syndicate, employed by Melani D'ian.

In 2387, Hassan assassinated Raimus on the planet Farius Prime. The person who employed Hassan was Melani D'ian, who herself took control of Raimus' portion of the Orion Syndicate.

In 2394, Hassan joined Melani on negotiations with the Klingon Chancellor J'mpok, where he was presented as being in charge, with Melani as his slave girl.

Following this, he moved his own base of operations to the former Orion homeworld in the Rigel system, where he could conduct Syndicate operations outside the Klingon Empire. This was presumed to be on the orders of Melani, who trusted him implicitly. (ST website: The Path to 2409)

Though his race is not stated, Hassan is implied to be Orion, by surviving the Syndicate purge (leaving mostly loyal Orions), his loyalty to Melani, and his occupation of the Orion homeworld. By apparent coincidence, his name also matches the Orion naming style described in the FASA RPG module: The Orions: Book of Common Knowledge.