In 'The Day Kasparov Quit', a book of interviews by Dirk Jan ten Geuzendam, Kasparov, just after losing the 2000 match to Kramnik, is quoted as saying (p.202),
[Kramnik] is the 14th World Champion. This is not Khalifman, Mattison, Bogoljubow, or whoever wins India. This is the man who joins Capablanca and the others.
What is the thread that ties these names -- Khalifman, Mattison, and Bogoljubow -- together?
Mattison: Mattison, Herman (1894-1932), Latvian player and study composer, known in Latvia as Matisons. In 1924 he won his country's first championship tournament and, later that year, ahead of Colle and Euwe, the first world amateur championship, arranged in connection with the Olympic Games at Paris. In the second and last amateur championship, organized by FIDE at The Hague in 1928, he took third prize after Euwe and Przepiorka, ahead of Becker. (Hooper & Whyld, 'Oxford Companion', p.252)
Bogoljubow: After Alekhine's victory over Capablanca , FIDE, for which the conducting of the World Championship was an eternally sore point, decided to establish its own championship in a match of ten games and to declare him the official contender to the throne. The participants in the 'candidates match', held in the spring of 1928 in Holland, were Bogoljubow, the winner of the super-tournament at Moscow 1925 and Euwe, supported by his 'committee'. This was a battle of equals: after a win in the sixth game the Dutchman was a point ahead, but in the end he lost by the minimal score: 4.5-5.5 (+2-3=5). (Kasparov, 'Predecessors II' [chapter on Euwe], p.20) See also FIDE Championship (1928) (Chesshistory.com).
Khalifman: 1999 FIDE Las Vegas (Khalifman 1st)
Anand (winner at India): 2000 FIDE India/Iran (Anand 1st)