-- He was the ultimate cold warrior, humbling the mighty Soviet chess establishment through his genius and a pounding ambition to be the best player in the world.

At a time when competition with the Soviets was being measured in moon landings and missile counts, Bobby Fischer proved that the United States could master an intellectual battlefield where knights and kings clashed on a black-and-white board.

But his own government once believed that he and his closest relatives might be Soviet spies.

FBI documents obtained by the Philadelphia Inquirer under the Freedom of Information Act show that intermittently, from the 1940s to the early 1970s, the Fischers were being watched.

The FBI worried that the Russians had tried to recruit the young chess prodigy in a trip he made to Moscow in 1958.

Agents also suspected that his mother, Regina, might have been a Soviet operative.

J. Edgar Hoover's agents interviewed informants, posed as student journalists and considered cultivating other chess players. They hounded Fischer's mother, reading her mail, questioning her neighbors, studying her canceled checks.

The FBI concluded that Regina Fischer was no spy, and that the Soviets had not tried to recruit her son.

But the FBI files and other documents offer insights into long-buried secrets about who Bobby Fischer is and who his parents were.

Fischer's father has widely been identified as German biophysicist Hans-Gerhardt Fischer. But documents suggest it was someone else. The FBI kept a file on that man, too.

The files offer glimpses into the world of Hoover's FBI, where agents in the Cold War pursued citizens of leftist leanings with a fevered intensity and few restraints.

Now 59, Bobby Fischer has become a reclusive, anti-Semitic expatriate. Efforts to interview him for this article were unsuccessful.

He has been seen in Japan, Hungary and the Philippines. In a Philippine radio interview Sept. 11, 2001, he applauded the terrorists' attacks and said America should be "wiped out."

Chess experts have analyzed Fischer's games in astonishing depth. Even the offhand games he played blindfolded have been exhumed and published like lost works of literature.

But his life is largely a mystery. Bruce Pandolfini, a noted chess teacher who was featured in the movie "Searching for Bobby Fischer," said of Fischer's beginnings: "Nothing is known."

Regina Fischer's 750-page FBI file is publicly available because she is deceased. A pediatrician, she died of cancer in 1997.

The file touches only a sliver of her son's chess career -- a trip he took to Moscow in 1958, when he was the champion of U.S. chess at 15. But it offers sweeping detail about the Fischer family's origins, friends and associates.

Regina Fischer's German husband, Hans-Gerhardt Fischer, had fought the fascists in the Spanish civil war in the 1930s. Her close Hungarian friend, Paul Nemenyi, specialized in fluid mechanics -- a field important to the design of airplanes and bombs. The FBI maintained that both men harbored communist sympathies.

Regina Fischer spoke eight languages. She was brilliant but paranoid, a psychiatrist determined in 1943. Then again, she really was being followed.

She raised Bobby in Brooklyn. They were poor; in a 1952 letter, she said she couldn't come up with money to patch 9-year-old Bobby's torn shoes.

The FBI began watching her and her circle in the 1940s. The last entry in her file is in 1973, when agents noted her opposition to the Vietnam War. Some orders in the file came straight from Hoover's office.

In the 1930s, while in her teens, she moved from the United States to Germany and then Russia, where she lived from 1933 to 1938 under Stalin. She attended medical school there.

In 1942, someone went through her papers, found politically tinged letters, and telephoned the FBI..

The FBI learned in 1957 that Regina Fischer had contacted the Soviet Embassy to discuss the trip her son would take the next year for matches in the Soviet Union.

Before Bobby Fischer left for Russia, an agent posed as a college journalist to interview producers of the TV show "I've Got a Secret." Bobby had been a guest and won plane tickets to Russia. (His "secret": He was U.S. chess champion. The panel was stumped.)

Despite playing well in Moscow, Fischer was peeved at not being matched with the Soviets' best.

The FBI heard from another informant: Fischer had called his mother in the United States and told her, "It's no good here."

Agents weren't sure what to make of that. So they guessed.

"[I]t is possible that the Soviets may have made an approach to Robert Fischer to which the youth took exception," Hoover's office wrote to the New York field office in September 1958.

The next month, New York agents reported that Fischer was a moody adolescent who didn't get along with his mother.

Who was Fischer's father?

Agents made it their business to find out. They checked his birth certificate; it listed his father as Gerhardt Fischer. He and Regina Wender had married in Moscow in 1933.

They divorced in 1945, two years after Bobby's birth, but the FBI believed they had been apart longer than that. Regina Fischer came here in 1939; the FBI said her husband never entered the United States.

The FBI seemed to pay more attention to her Hungarian friend, Nemenyi.

Nemenyi came to the United States in the 1930s, taught college mathematics and met Regina Fischer in 1942, according to the files. An informant told the bureau that in 1947, Nemenyi opined that Russia's system was "superior to that of the U.S."

Nemenyi also took a deep interest in Bobby Fischer. He paid child support and complained to social workers about the way Regina was raising the boy.

A social worker told the FBI of interviewing Nemenyi in 1948. The informant reported that as they spoke about Regina Fischer, Nemenyi had wept.

The heavily censored files don't say if Nemenyi was Fischer's father. Letters obtained by the Inquirer offer an answer. They are the papers of Nemenyi's late son Peter, a civil-rights activist who gave them to a state archive in Wisconsin.

"I take it you know that Paul was Bobby Fischer's father," Peter Nemenyi wrote after his father's death in 1952. The papers also include a plaintive letter that same year from Regina Fischer to Peter Nemenyi.

"Bobby . . . was sick 2 days with fever and sore throat and of course a doctor or medicine was out of the question," she wrote. "I don't think Paul would have wanted to leave Bobby this way and would ask you most urgently to let me know if Paul left anything for Bobby."