Euwe.
Weakest World Champ
Alexander Khalifman.
Although I object against the title 'weakest' world champ. Whoever got the title once, was not a weak player. I prefer 'least convincing'.
one brilliant game does not cover the weakness of losing to Fisher
Do you want me to bring up every game that Spassky won versus Fischer?
My issue with your comment was that you said Spassky was the weakest world champion 'by far'. And that losing to Fischer (who would have at have beaten anyone at that time) somehow makes him the weakest champion.
spassky by far who lost to fisher
Is that why his peak rating for several different time periods (1, 2, 3, 4, 5,10, 15 and 20 yrs) is higher (on some of these lists) than that of Euwe, Tal, Morphy, Steinitz... and Fischer (on the 20 yr peak performance list)?
http://www.chessmetrics.com/cm/CM2/PeakList.asp?Params=199510SSSSSWS000000000000111000000000000010100
Emanuel Lasker because when he lost the title to Capablanca Lasker gave up the match before its full games came to an end.
Alexander Khalifman.
Although I object against the title 'weakest' world champ. Whoever got the title once, was not a weak player. I prefer 'least convincing'.
I think we're only counting unified world champions, otherwise this would be easy.
Emanuel Lasker because when he lost the title to Capablanca Lasker gave up the match before its full games came to an end.
Peak Average Rating: 20 yr peak
| #1 | Garry Kasparov | 2856 | 1984-Jan through 2003-Dec |
| #2 | Anatoly Karpov | 2818 | 1977-Jan through 1996-Dec |
| #3 | Emanuel Lasker | 2809 |
|
Peak Average Rating: 15 yr peak
| #1 | Garry Kasparov | 2862 | 1987-Jan through 2001-Dec |
| #2 | Anatoly Karpov | 2820 | 1977-Jan through 1991-Dec |
| #3 | Emanuel Lasker | 2816 | 1890-Jan through 1904-Dec |
Peak Average Rating: 10 yr peak
| #1 | Garry Kasparov | 2863 | 1986-Jan through 1995-Dec |
| #2 | Emanuel Lasker | 2847 | 1893-Jan through 1902-Dec |
He's also in the TOP TEN for 1, 2, 3, 4, and 5 yr peaks
are you trying to baffle us with statistics...we have made up our minds dont confuse us with the facts
Do you know there was a Vera Menchik club. One GM suggested this club for all players who did not win a game against the (first?) Woman World Champion. This "club" grew rapidly! 
are you trying to baffle us with statistics...we have made up our minds dont confuse us with the facts
That has to be irony... Please tell me that's irony 
Spassky was underrated, he beat Petrosian in a match and even gave Fischer a real fight. All round great player

spassky by far who lost to fisher!
This Spassky?