Motown's ultimate love god, Marvin Gaye, has to be one of the most complex and fascinating characters ever to come out of the legendary Detroit record company.

''One of the most musically creative minds ever,'' his colleague Smokey Robinson says of Gaye in a new PBS documentary, Marvin Gaye: What's Going On, that airs tonight at 9 on WNEO/WEAO (Channels 45/49) and at 10:30 on WVIZ (Channel 25). ''He was also a very troubled man.'' Gaye's life and career epitomized the highest highs and lowest lows that befell any Motown artist. His 1968 hit I Heard It Through the Grapevine became the longest-running Motown No. 1 hit ever (seven weeks) and his 1971 album What's Going On is widely considered a masterpiece.

But Gaye led a tumultuous, drug-fueled life. His earliest family life was dysfunctional, and it played out in his death at the hands of his father, the Rev. Marvin Gay Sr., who shot him in 1984, the day before his 45th birthday.

For this documentary, producers were able to talk to Motown founder Berry Gordy Jr., who famously opposed the release of What's Going On at first (''I was petrified he was going to ruin his image,'' Gordy says). Among the others who speak on camera are the singer's second wife Janis (mother of his daughter Nona and son Frankie), his sister Jeanne, Motown singers Kim Weston, Mary Wilson, Bobby Taylor and Gladys Knight, and his biographer (Divided Soul) David Ritz.

Born in Washington, D.C., Gaye (who added an ''e'' to the family name) started singing in his father's church. He came to Detroit in 1960, slogging away at Motown for several years as a drummer and then, trying to make it as a suave, finger-snapping Rat Pack wannabe. Once he gave up the dream of being a sepia Sinatra, Gaye finally hit with soulful pop hits like Hitchhike and Pride and Joy.

Along the way, he married Anna Gordy, Berry Gordy's chic older sister (some 15 years Gaye's senior). In clips from an interview done late in his life, Gaye admitted that he took full advantage of his in-law status as the prince of Motown.

''I enjoyed being able to say, I don't have to do that . . . you guys do that,'' Gaye says, laughing.

Gaye's relationship with his mother was very close; she was his protector from his eccentric, often hostile, pastor father. Friends and relatives describe Gaye's bewilderment over his father's habit of cross-dressing, and how it affected the younger man psychologically, spurring him to overcompensate by womanizing and throwing himself into competitive sports.

Interestingly, Gaye admits in an interview clip that he sometimes had ''semi-violent disagreements'' with his brother-in-law/boss Gordy.

Torn musically and personally between the pleasures of the flesh and spirituality, Gaye was a living, breathing mass of contradictions.

His handsomeness impressed every woman he met, but the singer couldn't dance ''a lick,'' as his Motown friends laughingly recall, and as the film clips bear out.

Fortunately, when Motown teamed Gaye up to sing duets with Tammi Terrell, he didn't have to dance at all, just tower over the petite dynamo, gaze into her eyes and sing.

Songwriter/producer Nick Ashford described why they worked so well together: ''She was very sassy, and he had that growl in his voice . . . ''

Terrell's death from a brain tumor in 1970 haunted Gaye to the end of his days. His downward spiral into drugs and alcohol, leading to his violent final confrontation with his father, is documented here.

It's bittersweet, because after some years off, including a stint living in a bread truck in Hawaii, Gaye was able to rally enough to produce Sexual Healing in 1982, which earned him two Grammys — incredibly, his first ever.

The world, and Gordy, caught up with the greatness of that album.

''Probably the greatest piece of music Motown put out,'' the Motown chairman says.