Michael Gregor (also known as Silenius) is an Austrian musician who is currently in the bands Amestigon (since 1998) as vocalist, Kreuzweg Ost as programmer, and Summoning as vocalist, keyboardist, and bassist; the two latter bands are bands that he is a founding member of. He supplied vocals for Abigor from 1994 to 1999 and appeared on seven of Abigor's releases. Silenius was vocalist and keyboardist for Pazuzu and played on the band's split album and debut album. Along with fellow Summoning bandmate Richard Lederer, Silenius also used to be a member of Die Verbannten Kinder Evas, serving as a vocalist and a keyboardist. Silenius has recorded music for a project called "Mirkwood", of which no material has yet been released.
Considering the fantasy-related lyrical content of Summoning, Michael Gregor has explained that he has been interested in the works of J. R. R. Tolkien since age 16 or 17, but was interested in fantasy literature since his childhood.