Started as a guitarist/vocalist in helloween probably the most influencial euro power metal band. Unhappy with his vocal talents, helloween hired a new vocalist Michael Kiske...With his unbelievable voice Helloween were becoming a force to be reckoned with
Kai Hansen then left at the worst possible time , just after releasing the two greatest Helloween albums "Keeper of the seven key" Parts I + II ... Helloween were in their prime but without Kai Hansen
He then founded gamma ray but started only as a guitarist. After the departure of Ralf Sheepers(vocals) Kai took on the position of vocals and guitar again , He also founded iron savior another Power metal band with a very different vocalist in Piet Sielck.
Kai Hansen is still with gamma ray and has worked with French Power Metal band Heavenly...Swedish band hammerfall ... power metal icons blind guardian ... and the project of tobias sammet avantasia along with members from old band helloween and other greats from the power metal genre.