Gamma Ray
Kai Hansen formed Gamma Ray after leaving Helloween in 1989. Originally just a project involving Hansen, Ralf Scheepers and some guest musicians, Gamma Ray soon evolved into a full-time band.

In 1994, Ralf Scheepers left Gamma Ray as a result of living too far away from the base camp, so Kai Hansen took over the singing just like on the first Helloween album. It has also been suggested that Scheepers left hoping to join Judas Priest, who were looking to replace Rob Halford around that time, and when that didn't work out he formed his own band with Mat Sinner, Primal Fear.

Dirk Schlächter, though originally a bass player, joined as a guitarist, then switched to bass seven years later.

Following line-up instability in the band's early days, the Somewhere Out in Space line-up of Hansen, Schlächter, Richter and Zimmermann assembled in 1997 and stayed together for 15 years until Zimmermann left the band for a more settled lifestyle in 2012.

In 2006, Henjo Richter was injured in a fall and replaced on tour by Kasperi Heikkinen of the Finnish Gamma Ray tribute band Guardians of Mankind, whose keyboard player Eero Kaukomies was already part of the Gamma Ray touring line-up. Eero was also drafted in as a temporary live member of Freedom Call around the same time, whose ex-keyboard player Nils Neumann had also been a live member of Gamma Ray.

Henning Basse filled in as vocalist on January 17th and 18th of 2008 when Kai Hansen was suffering from flu. Kai still performed in his role as guitarist.

Frank Beck first joined as a live member in 2014, singing several songs. He was inducted as a band member on Halloween 2015 to ease Kai Hansen's touring duties and "give the band a new dimension sound-wise".