One of Grateful Dead legend Jerry Garcia’s most famous guitars is going back on auction, where it could fetch more than $1 million to back a civil rights group. Known as Wolf, the electric guitar was custom-made by luthier Doug Irwin. Garcia debuted it at a 1973 concert in New York before the instrument — along with Hell’s Angels bikers — became ever-present during the Dead’s perpetual touring.

Dan Pritzker, a music-loving philanthropist who is an heir to the wealthy Chicago family known for the Hyatt hotel chain, bought Wolf for $789,500 from the auction house Guernsey’s in 2002. Pritzker, who occasionally loaned the guitar to musicians, decided to put it back on auction, announcing that all proceeds would go to the Southern Poverty Law Center, which wages legal battles against white supremacists and other hate groups.

“He called me three months ago to say he was concerned about the divisive things that are going on in the country and wanted to do something meaningful,” Guernsey’s president Arlan Ettinger said. The Southern Poverty Law Center has voiced alarm at a spike in hate crimes, especially targeting immigrants and Muslims, since President Donald Trump launched his campaign in 2015.

“As extremism moves from the fringe to the mainstream, we have a lot of work to do,” the Alabama-based center’s president, Richard Cohen, said in a statement. “This remarkable act of generosity only strengthens our resolve,” he added of the guitar sale.

Guernsey’s will sell Wolf at a May 31 concert at the Brooklyn Bowl music venue, to which the auction house is hoping to draw major artists. Online bids will also be accepted. Ettinger said it was difficult to estimate Wolf’s sale price, but that it could near record territory.

Wolf was last sold alongside another guitar Irwin made for Garcia, Tiger, which fetched just under $1 million, a record at the time. In 2015, the Gibson on which John Lennon played “Love Me Do” and other early Beatles songs sold for $2.4 million, another record for a historic guitar.

Formed near San Francisco, The Grateful Dead became one of the emblematic bands of the hippie era, drawing “Deadhead” fans who found a sense of community traveling from show to show to experience the ever-evolving jam rock.

Garcia, who died in 1995, bequeathed his famous guitars to Irwin, who had become destitute. After initial objections from the rest of the band, the luthier took control and put the instruments on auction.