Aslan is the Lion Guardian of the Beams and the beam counterpart of Garuda. It is around Aslan's beam that Tim Ross encounters Maerlyn, who was turned into a tyger by The Covenant Man. Maerlyn tells Tim that The Covenant Man chose this form for him, because he probably wasn't smart enough to replicate a beam guardian.
Aslan is named after the lion from C.S. Lewis' The Chronicle of Narnia series.