I. THE UNOFFICIAL WORLD CHAMPIONSHIP

The first official match specifically designated as being for the World's Championship was held in 1886 between William Steinitz of the USA, and Johanes Zukertort of Poland. Steinitz had been the world's strongest active player for about 20 years, but no one dared to hold a championship match while Paul Morphy, an American who had dominated the world scene for a year and then retired, was still alive.

Upon the death of Morphy in 1884, Steinitz arranged a match with his strongest rival, with the stipulation that the winner should be considered World Champion. The "official" line of champions begins at that time. However, before 1886, there were several players generally regarded as the strongest players of their eras, whom many writers regard as "Unofficial World Champions". Here is one such possible list. Names and dates can be highly conjectural, so don't write to complain if you don't like the list. That's what "unofficial" means.

II. THE IMPERIAL WORLD CHAMPIONSHIP

With the Steinitz-Zukertort match of 1886, the line of "Official" World Champions begins. At this time, the title was more or less the personal property of the holder, who could more or less name whatever conditions he wished, against whatever opponent he liked.

III. THE FIDE UNDISPUTED WORLD CHAMPIONSHIP

When World Champion Alexander Alekhine died in 1946, on the eve of a title defense against Mikhail Botvinnik, the World Chess Federation, founded in 1924, stepped in and administered the title themselves. Max Euwe, the only surviving former champion was their first World Champion, for a single day, before the Soviet delegation arrived and anulled the decision to crown him. A World Championship tournament was then held in 1948 to name a new champion.

After this began a series of 3-year World Championship Cycles. The world was divided up into various "zones", some consisting of one country, others of more. Each zone was alotted a certain number of championship contender spots, and held a zonal tournament to decide who would win them, and be sent to an "Interzonal" tournament of all such contenders in the first year of the cycle. In the second cycle year, the top qualifiers from the Interzonal tournament (or tournaments, in later years there was more than one Interzonal) played in a Candidates Series, which was sometimes a tournament, sometimes a series of matches, and on one occasion, both. The winner of the Candidates Series would challenge the World Champion to a match in the 3rd year of the cycle.

In Cycles 1-4, and 10-15, a defeated Champion had the right to challenge his conqueror to a re-match in the first year of the next cycle.

IV. THE IMPERIAL CHAMPIONSHIP RETURNS

When Kasparov and Short played their 1993 World Championship Match outside of FIDE, the title returned to the Imperial Championship days. There were various briefly-lived organizations, such as the PCA, nominally in charge of determining a challenger, but largely, the champion could do as he pleased.

V. ROLL CALL OF OFFICIAL WORLD CHAMPIONS

As you can see, there are a few differences between this list and the ones you normally see published. Here are the controversial points:

Most sources do not recognize (or remember) Lasker's resignation of the title in 1920, and so consider him to have reigned until 1921.

Most sources do not recognize (or remember) Euwe's one day title reign in 1946.

Most sources do not recognize (or remember) that Fischer resigned the World Title in 1974, and so consider him to have reigned until 1975.

And finally, most people do not remember that William Steinitz was the first American World Champion, and so give that honor to Fischer. This may be due to Steinitz's nickname, "The Austrian Morphy", which has helped to obscure the fact that Steinitz had acquired US citizenship before winning the title in 1886, and held it throughout his entire World Championship reign.