Lorien is the only member of his species living in the galaxy in the 23rd century, the others having died of various causes or left known space to explore "beyond the rim".
Lorien is a being composed principally of energy, although he can adopt a humanoid physical form without difficulty. He is ageless, being as much older than the First Ones as they are older than the Young Races.
Lorien can manipulate energy in unspecified ways. His most demonstrable feat is reviving John Sheridan, whose body had been damaged beyond any ordinary healing by a nuclear explosion and a long fall. Lorien's influence sustained Sheridan in normal health for about twenty years.
Little is known about Lorien's activities prior to the final Shadow War of 2260. He was known to be dwelling deep below the surface of the planet Zha'Ha'Dum by that time, and he was awakenend when John Sheridan visited the planet and detonated two 500-megaton bombs in the capital city of the Shadows.
Lorien found Sheridan's dying body and revived him, then traveled with him to Babylon 5 to advise him in ending the Shadow Wars once and for all. When the Vorlons and Shadows agreed to leave the galaxy to allow the Young Races to develop on their own, Lorien went with them, returning only to collect Sheridan's body at the time of his death.