Slipknot's Paul Gray, shown here in his trademark pig mask, has died at the age of 38. (Mark J.Terrill/Associated Press)

Slipknot bassist Paul Gray was found dead in an Iowa hotel on Monday.

The Des Moines Register reported that police found no evidence of foul play in the 38-year-old heavy metal musician's death.

Gray, who lived in Johnston, Iowa, had stayed at the hotel in nearby Urbanville before, the newspaper said. He was described by hotel staff as being a quiet and respectful guest.

An autopsy that took place on Tuesday failed to determine how Gray died. Police said it could be up to six weeks before toxicology results are available that could determine the cause of his death.

Dozens of bands have paid tribute to Gray over the internet since reports of his death surfaced.

In a post on Twitter, Good Charlotte's Benji Madden wrote: "RIP Paul Gray sendin' thoughts & prayers out to Slipknot and their friends & families."

Gray formed Slipknot in 1995 with percussionist Shawn Crahan and drummer Joey Jordison, and was known as its core, if occasionally errant, member.

The heavy metal band has been nominated for seven Grammy Awards, taking home a Grammy in 2006 for Best Metal Performance.

Slipknot's members wore masks on stage. Grey chose a pig mask and was affectionately known as The Pig.

The Guardian said his death "signals the end of the Iowan band's classic lineup."

Gray had a history of drug abuse. In 2003, he was arrested for possession of cocaine and marijuana paraphernalia, as well as a red light violation after crashing his Porsche into another motor vehicle in Des Moines. He was sentenced to one year of probation. But Rolling Stone noted he seemed to have turned his life around in recent years.

Two years ago, he married his girlfriend, Brenna Paul.

She is expecting their first child later this year.