John Warren Geils Jr. was found dead in his Groton, Massachusetts home, according to ABC Boston affiliate WCVB.
Geils formed the Boston-based band in the 1960s as an acoustic blues trio. They later added singer Peter Wolf and became more blues-rock oriented, signing their first record deal in 1970. Their 1970s hits included covers of "First I Look at the Purse" and "Lookin' for a Love" and original tunes "Give it to Me" "Must of Got Lost."
But the group hit its peak in 1981 with its more pop-oriented album Freeze Frame, which hit No. 1 led by the singles "Centerfold," "Freeze Frame" and "Angel in Blue."
The band broke up in 1985 and Geils turned to other interests, including racing and restoring cars.
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They had occasional reunions, including a tour in 1999. But Geils later broke from the other band members, who continued to perform under the J. Geils Band name without him, triggering a legal fight over the name in 2012.
The Groton Police Department says officers who were called for a well-being check found Geils dead in his home around 4 p.m. The department is investigating, but said the preliminary indication is that he died of natural causes.