Former Weezer bassist Mikey Welsh was found dead at the Rafaello Hotel in Chicago on Saturday afternoon. He was 40 years old.

Hotel staff found the musician and painter unresponsive and not breathing. They had come to his room to see why Welsh hadn't checked out of the hotel.

Welsh played with Weezer from 1998 to 2001 and was on the band's enormously popular self-titled album (also known as The Green Album).

He was visiting Chicago to see Weezer play at RiotFest, and was reportedly excited to see his former band-mates.

It saddens me and the guys in Weezer so much to say that our beautiful, creative, hilarious and sweet friend Mikey Welsh has passed away at the very young age of 40. A unique talent, a deeply loving friend and father, and a great artist is gone, but we will never forget him. His chapter in the weezer story ('98 - '01) was vital, essential, wild, and amazing, Weezer said in a statement on their Web site.

Despite a rich artistic career, Welsh had a number of personal troubles. He left Weezer after an attempted suicide and mental breakdown in 2001.

“Basically, a lifetime of doing drugs and being undiagnosed as having post-traumatic stress disorder and borderline personality disorder finally caught up with me when I was 30 years old,” Welsh said in a 2007 interview. “At the beginning of a 3-month European tour with Weezer, I started slowly falling apart.”

The cause of death has yet to be determined, but police suspect that Welsh died of a drug overdose.