Kai Michael Hansen (born January 17, 1963, in Hamburg, West Germany) is a power metal guitarist and vocalist.

Serving as founding member, lead guitarist, and vocalist of power metal band Helloween, and his own formed band Gamma Ray, Kai Hansen has been proven to be one of the most influential figures in power metal, and has sold millions of albums worldwide.

His musical career started in 1978 in a band called Gentry, alongside Iron Savior's co-founder and producer Piet Sielck. In 1983 he and Michael Weikath founded Helloween, where he was guitarist and singer until Michael Kiske took over the microphone for the albums "Keeper of the Seven Keys Part 1" and "Keeper of the Seven Keys Part 2". Hansen left the band due to the extensive touring in 1988-89 and went on to form his own power metal band Gamma Ray. Hansen also joined Iron Savior as guitarist in 1997, but quit after a few years to focus his efforts on Gamma Ray. He has now forged a very successful career with Gamma Ray, releasing several albums and playing sold out tours across the globe.

Kai participated in a large number of other projects. He appeared as a guest vocalist on Blind Guardian's albums "Follow the Blind" and "Tales From the Twilight World". Together with HammerFall he recorded a cover version of Helloween's "I Want Out". Kai played the role of Regrin the dwarf in Avantasia rock opera by Tobias Sammet.

In 2005, he toured with the young German power/viking metal band Stormwarrior from his home town of Hamburg as lead singer, playing material from his classic Helloween debut album "Walls of Jericho" - the favorite album and greatest influence of Stormwarrior. "Stormwarrior featuring Kai Hansen" returned in 2007 to play at the Magic Circle Festival in Bad Arolsen and at the Wacken Open Air Festival.

In 2008 Kai Hansen featured Stormwarrior at Sweden Rock Festival 2008.