Wilson spent much of the ’70s battling a cocaine addiction and was eventually diagnosed with bipolar disorder (also known as manic-depressive disorder) and with schizoaffective disorder, a condition that can cause the afflicted to become paranoid and hear voices.

As stories spread about his strange behavior, the media routinely labeled Wilson a “mad genius,” as if his mental problems were the wellspring of his amazing talent. “People like to build this romantic story of the tortured poet-freak whose music has some great magical quality because he’s damaged,” says the Flaming Lips’ Coyne, who interviewed Wilson in 1999 for an HBO program that never aired. “They don’t want to think that the real reason his music is magical is because he worked hard at it for long hours.”

Love says his cousin is brilliant in spite of the mental illness. “But it can manifest itself in some pretty fantastic ways,” he says. “If you’re manic and totally energetic in the studio, that’s when you might come up with ‘Fun, Fun, Fun’ or ‘I Get Around.’ And if you’re in a more melancholy state, that might lead to some beautiful haunting melodies, like ‘God Only Knows.’ ”

Wilson was estranged from the Beach Boys for long periods after 1971. The band struggled without its creative mastermind and suffered another blow in 1983 when drummer Dennis Wilson died in an alcohol-related drowning accident.

In the late 1980s and early ’90s, Brian’s family successfully took legal action to separate him from Dr. Eugene Landy, the Svengali-like around-the-clock therapist who also became Wilson’s business and songwriting partner. Carl Wilson, the band’s de facto road leader in Brian’s absence, died of cancer in 1998, leaving Love to steer the Beach Boys — sometimes with help from his lawyers.

Love was forced to sue Brian Wilson in 1992 over songwriting credit and royalties (Love won), and he sued his cousin again in 2005 for using the band’s name to market a solo album (the case was dismissed). He also sued Jardine for touring as The Beach Boys Family & Friends; since settling that case out of court in 2008, Love has been the sole original member touring as the Beach Boys.