Chess right of a deposed champion to a rematch, and the next champion, Armenian Tigran Petrosian, a player renowned for his defensive and positional skills, held the title for two cycles, 1963–1969. His successor, Boris Spassky from Russia (champion 1969–1972), won games in both positional and sharp tactical style. The next championship, the so-called Match of the Century, saw the first non-Soviet challenger since World War II, American Bobby Fischer, who defeated his Candidates opponents by unheard-of margins and clearly won the world championship match. In 1975, however, Fischer refused to defend his title against Soviet Anatoly Karpov when FIDE did
Bobby Fischer makes him tick" and described him as "a troubled human being" with "obvious personal problems". Valery Krylov, advisor to Anatoly Karpov and a specialist in the "psycho-physiological rehabilitation of sportsmen", believed Fischer suffered from schizophrenia. Psychologist Joseph G. Ponterotto, from second-hand sources, concludes that "Bobby did not meet all the necessary criteria to reach diagnoses of schizophrenia or Asperger syndrome. The evidence is stronger for paranoid personality disorder." Magnús Skúlason, a chess player, psychiatrist and head doctor of Sogn Mental Asylum for the Criminally Insane, befriended Fischer towards the end of Fischer's life. From "Endgame", Fischer's 2011 biography by Frank