Who is/was the lowest ranked World Chess Champion?

Question

Boris Gelfand has just won the 7th of 12 games (all previous drawn) in the FIDE World Championship match against the current holder of the title Viswanathan Anand. This puts him in a good position to take the title. Gelfand is currently ranked 20th in the world; over the past decade he has averaged approximately 13th in the world (FIDE rankings).

If Gelfand does win, will his low ranking be without precedent or is this a common match-play aberration? Who has been the lowest ranked on the FIDE rankings list at the time of taking the title of World Chess Champion?

Answer 1

To answer my own question, numbers shown in bold below are the FIDE ranking of the player at the time they were crowned World Champion. Before 1964 there was no ranking system as far as I know. Ranking taken from FIDE rankings site and this chess USA education webpage.

Undisputed world champions 1886–1993
?? Wilhelm Steinitz (1886–1894)
?? Emanuel Lasker (1894–1921)
?? José Raúl Capablanca (1921–1927)
?? Alexander Alekhine (1927–1935, 1937–1946)
?? Max Euwe (1935–1937)
?? Mikhail Botvinnik (1948–1957, 1958–1960, 1961–1963)
?? Vasily Smyslov (1957–1958)
?? Mikhail Tal (1960–1961)
01 Tigran Petrosian (1963–1969) (first unofficial rankings list 1964)
02 Boris Spassky (1969–1972)
01 Bobby Fischer (1972–1975)
02 Anatoly Karpov (1975–1985)
02 Garry Kasparov (1985–1993)

Classical (PCA/Braingames) world champions 1993–2006
01 Garry Kasparov (1993–2000)
03 Vladimir Kramnik (2000–2006)

FIDE world champions 1993–2006
02 Anatoly Karpov (1993–1999)
44 Alexander Khalifman (1999–2000)
02 Viswanathan Anand (2000–2002)
07 Ruslan Ponomariov (2002–2004)
54 Rustam Kasimdzhanov (2004–2005)
03 Veselin Topalov (2005–2006)

Undisputed world champions 2006–present
09 Vladimir Kramnik (2006–2007)
01 Viswanathan Anand (2007–present)

Next undisputed world champion ?
04 Viswanathan Anand
20 Boris Gelfand

And as I write this Anand has won game 8.

Also, an interesting quote from Alexander Khalifman responding to his very low ranking at the time of his crowning FIDE world champion in 1999:

"Rating systems work perfectly for players who play only in round robin closed events. I think most of them are overrated. Organizers invite the same people over and over because they have the same rating and their rating stays high."

Of course he would say that but perhaps some truth there.

Answer 2

According to this page, the weakest world champions would be Euwe and Steinitz. The list is old, but we've had nothing but powerhouses since 1978.

Answer 3

It would depend entirely on how they were ranked.

I think you meant "rated" instead of "ranked" but nevertheless elo ratings are relatively recent so we can't really compare older players.

If I were to guess I would say Euwe. Nobody expected him to beat Alekhine.