He is best known for his time in the power metal band Helloween,[1] with which he played for twelve years, after replacing founding member Kai Hansen.

He was then fairly inactive musically, and made a living as a car mechanic until Michael Weikath called him to offer him a position in Helloween in 1989.

"[4] Grapow played on the Helloween albums Pink Bubbles Go Ape, Chameleon, Master of the Rings, The Time of the Oath, High Live, Better Than Raw, Metal Jukebox, and The Dark Ride.

In 2012, in an interview with Metal Shock Finland's chief editor Mohsen Fayyazi, Grapow stated: I felt very secure in Helloween.

I was telling the truth and that's how I am… It was a great time in Helloween… but I was happy when I left the band after the Dark Ride because it's one of my favourite albums, it totally changed my life.

[5][6]Grapow and Kusch decided to go on with the side project they had been planning and formed the band Masterplan with former Ark and the Snakes singer Jørn Lande.