There are two known (to me) 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 annual ly without a break since it was initiated in 1984. Some 182 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. (I regret to say that I came 42nd, but my excuse is that this group still uses 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 cultural activities 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 2016 Tournament

The XXIth Mind Sports Olympiad took place again at JW3 in London from August 20 to 29, 2016 and the Hare & Tortoise World Championship from 7pm of Wednesday 23rd. There were 17 competitors. Silver went to Martin Hobemagi (Finland), Bronze to James Heppell (England).
For the 2017 tournament rules see ht-mso.html. They will be revised for 2018 to cover some irregularities that occurred and to ensure that all four games, and the whole tournament, finish by 10.10pm at the latest.