There are at least two rival "World Championship" tournaments, one based in the UK and one in Germany.
The German one, centred on districts in the Ruhr valley, has been running annually since 1984. Some 200 competitors have taken part over that period. The venue varies, as it is customary for the winner of each event to host the next year's in their home town, and players come from all over the country. When I attended the one held in Ratingen in 2011 there was an entry list of forty-eight. (My excuse for coming 46th is that the group was then still using the 1978 Ravensburger board, to which I am no longer accustomed.) The whole event was a wonderful social occasion, the play sessions being interspersed with entertainments including talks, songs and general merry-making. A prominent young member of the play group is the multi-talented musician Tobias Krüger, who performs under the name MrTobiTill, and some of whose videos can be seen on YouTube - see, for example, "Beatsteaks".
The UK tournament is held annually as part of the Mind Sports Olympiad, initiated in 1997. There was a tournament in its first year, followed by a gap of nine years. The recorded winners are:

Mind Sports Olympiad 2018 Tournament

The XXIInd Mind Sports Olympiad took place again at JW3 in London from August 19 to 27, 2018 and the Hare & Tortoise World Championship from 6.45pm on Sunday 19th. For the latest tournament rules see ht-mso.html. They have been revised to obviate some irregularities that occurred in 2017 and to ensure that all four games, and the whole tournament, finish by 10.10pm at the latest. Which it did!