der Weltmeister
world champion
A person or team that has won first place in a world championship in a particular sport or discipline.
Max Verstappen wurde erneut Formel-1-Weltmeister.
Max Verstappen became Formula 1 world champion again.

world champion
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world champion
A person or team that has won first place in a world championship in a particular sport or discipline.
Max Verstappen wurde erneut Formel-1-Weltmeister.
Max Verstappen became Formula 1 world champion again.

The word 'Weltmeister' (world champion) is a simple compound of 'Welt' (world) and 'Meister' (master/champion). So it literally refers to a master or champion at the level of the whole world.
Die deutsche Nationalmannschaft wurde 2014 Fußball-Weltmeister.
The German national team became football world champion in 2014.
To name the sport or discipline in which someone is world champion, German uses the preposition 'in' followed by the dative.
Sie ist amtierende Weltmeisterin im Skifahren.
She is the reigning world champion in skiing.
This meaning is colloquial and almost always meant ironically or humorously. It is used to exaggerate an extreme, often negative, trait of a person.
Er vergisst immer alles, er ist wirklich Weltmeister im Vergessen.
He always forgets everything; he really is world champion at forgetting.
In the ironic meaning, 'Weltmeister' (world champion) is often combined with nominalized verbs that describe a bad habit. Typical examples are: 'Weltmeister im Jammern' (world champion at complaining), 'Weltmeister im Zuspätkommen' (world champion at being late), or 'Weltmeister im Ausredenfinden' (world champion at finding excuses).
Frag ihn nicht nach seiner Meinung, er ist Weltmeister im Kritisieren.
Don't ask him for his opinion; he's world champion at criticizing.
master / champion
'der Meister' and 'der Weltmeister' can both refer to a person or team that is especially successful. 'der Meister' is more general: it can be the winner of a championship, but also someone who can do something very well. 'der Weltmeister' is more specific and normally means the winner of a world championship. Colloquially, 'Weltmeister' can also be used ironically, for example for someone who constantly does something. The words can be confused in sports. The important point is: every 'Weltmeister' is a 'Meister', but not every 'Meister' is a 'Weltmeister'.

Am Wochenende ist der neue Weltmeister im Schwimmen nach Hause zurückgekehrt.
At the weekend, the new world champion in swimming returned home.
Nach dem letzten Spiel wurde die Mannschaft Meister der Liga.
After the final match, the team became league champions.