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David Sullivan dropped out of high school to manage a rock band in Mexico City and hung out on a Sioux reservation with a medicine man named Crow Dog.

He built military radar in Khadafy's Libya and stared down a notorious Brazilian drug lord in the slums of Rio. And he castrated bulls in Bolivia.

He was perhaps more well-known as a San Francisco private investigator with an expertise in infiltrating cults - from the globally influential to the small ones led by charismatic narcissists who more often than not were middle-aged, squeaky-voiced men with a big gut and poor personal hygiene.

Mr. Sullivan was either a real-life Don Quixote, a Hemingway-meets-Christopher Marlowe or a swashbuckling, life-loving, literary gumshoe, depending on the friend describing him.

Mr. Sullivan died Oct. 11 in his San Francisco home following a recurrence of cancer. He was 62.

Despite the diagnosis of a terminal illness, his death was unexpected and startled friends around the world, who believed he was larger than life.

Ready to travel

He had spent the night before watching Alfred Hitchcock's "Vertigo," and making plans to travel, said Jon Lee Anderson, a writer for the New Yorker, who met Mr. Sullivan at a Brazilian literary festival in 2005.

"He was in good form, living life to the fullest, full-breasted, full arms, all the way, no half measures," Anderson said. "He was the ultimate Huckleberry Finn."

Mr. Sullivan was born July 20, 1951, in Salina, Kan., to George and Virginia Sullivan, the youngest of three brothers. His father sold cars and ran other businesses and his mother worked in a pawnshop.

The family moved to Boulder, Colo., where Mr. Sullivan attended high school, but he ran off to Mexico at age 16 before graduating. He later earned his equivalency diploma and attended college at various universities, including the University of Guadalajara, to study pre-Columbian civilizations, which included stints at archaeological digs in Mexico and Peru.

He was also a senior advocate for the San Francisco Neighborhood Legal Assistance Foundation and later a group home supervisor for abused, abandoned and neglected youth as well as a licensing officer for the state Department of Health and Human Services investigating abuse of the elderly and disabled.

But it was a chance encounter with a private investigator in Mexico that offered Sullivan a new career path.

He took a job with San Francisco sleuth Hal Lipset, famous for his bugged martinis, to learn the craft.

After he opened his own agency, he worked on civil investigations related to undue influence and clergy and therapist abuse.

That's when he met Dr. Margaret Singer, a renowned author and psychologist, who recruited him into the world of psychological coercion and the world of cults.

Working on a memoir

He had an "appetite for life and the varied aspects of it," including the "shadowy worlds that make things go," said Joshua Jelly-Shapiro, a writer and geographer, who was working with Mr. Sullivan on his memoir.

He was ready to tell tales on the groups he had penetrated, the big and dangerous ones, Jelly-Shapiro said.

Think Scientologists and members of the Unification Church, or Moonies.

"He so wanted this book to happen," he said. "He was ready to pick a fight with those people."

He believed they were charlatans, Jelly-Shapiro said.

"He just really loathed the way these groups and people manipulated people and ruined lives," he said.

Mr. Sullivan had a deep sense of the importance of free will, he added.

He lived a life that demonstrated that every day, his friends said.

"In the end, he was a kind of archetypal American," Anderson said. "He's like one of those characters out of the West. They only come from America.

"A complete one-off."

Mr. Sullivan is survived by one brother, Michael Sullivan, of Salina, Kan.

A memorial is being planned for December.

Jill Tucker is a San Francisco Chronicle staff writer. E-mail: jtucker@sfchronicle.com