[qfikugag] Road to challenging for the championship

A list of challengers for the world chess championship, and a brief description of how they became challenger.

2014: Anand qualified into Candidates via losing 2013 championship
2013: Carlsen qualified into Candidates via rating
2012: Gelfand qualified into Candidates via World Cup
2010: Topalov seeded to challenger's match via winning 2005, losing 2006
2008: Kramnik right of rematch
2007 8-player round-robin: winner Anand qualified via 2nd place of FIDE 2005 championship
2006 reunification: Kramnik and Topalov via respective championships
2005 FIDE 8-player round robin: winner Topalov qualified via rating
2004 Classical: Leko invited to 8-player Candidates ("Dortmund Sparkassen Chess Meeting")
2004 FIDE 128-player single elimination: winner Kasimdzhanov probably invited via rating
2002 FIDE 128-player single elimination: winner Ponomariov probably invited via rating
2000 FIDE 100-player single elimination: winner Anand invited via rating, seeded to second round
2000 Classical: Kramnik handpicked by Kasparov
1999 FIDE 100-player single elimination: winner Khalifman (not specially seeded, though others were)
1998 FIDE 100-player single elimination: winner Anand seeded to second round
1996 FIDE 13-player single elimination: winner Karpov seeded into semifinal
1995 Classical: Anand via Interzonal (called "Qualifying Tournament")
1993 FIDE: Timman via Interzonal, Karpov seeded into second round of 15-player single elimination Candidates. Both had lost to Short.
1993 Classical: Short via Interzonal
1990: Karpov seeded into second round (quarterfinals) of 15-player single elimination
1987: Karpov seeded into challenger match
1986: Karpov right of rematch
1985: Kasparov via restart of abandoned match
1984: Kasparov via Interzonal
1981: Korchnoi seeded into Candidates via losing previous championship
1978: Korchnoi seeded into Candidates via runner up of previous Candidates
1975: Karpov via Interzonal
1972: Fischer via Interzonal (though entered Interzonal tournament only because Benko voluntarily gave up his spot)
1969: Spassky seeded into Candidates via losing previous championship
1966: Spassky via Interzonal
1963: Petrosian via Interzonal
1961: Botvinnik right of rematch
1960: Tal via Interzonal
1958: Botvinnik right of rematch
1957: Smyslov seeded into Candidates via losing previous championship
1954: Smyslov seeded into Candidates via being in top 8 of previous Candidates
1951: Bronstein via Interzonal
1948 inaugural: winner Botvinnik via invitation to 1938 AVRO.

The inspiration for compiling this list: Almost always, the reigning champion qualifies for the next championship match, and we accept this as a matter of course.  However, rather frequently, the challenger has also had an easier route to become challenger than all the other potential challengers.  Nevertheless, 2000 Classical was an instance of a challenger chosen in seemingly the most corrupt way, yet resulting in an amazing match with surprising result.