der Papst
pope
The head of the Roman Catholic Church and of the state of Vatican City.
Der Papst hält zu Ostern eine besondere Messe im Petersdom.
The pope holds a special Mass in St. Peter's Basilica at Easter.

pope
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pope
The head of the Roman Catholic Church and of the state of Vatican City.
Der Papst hält zu Ostern eine besondere Messe im Petersdom.
The pope holds a special Mass in St. Peter's Basilica at Easter.

The word 'Papst' (pope) is often used like a title directly before the person's name. In this case, it is used without an article.
Papst Franziskus besucht nächstes Jahr Deutschland.
Pope Francis is visiting Germany next year.
In the figurative meaning of 'Experte' (expert), 'Papst' (pope) is often combined with a field of expertise. This can happen as a compound noun, e.g. 'Literaturpapst' (literary pope / leading literary authority), or with the genitive.
Er gilt als der Fitness-Papst in den sozialen Medien.
He is considered the fitness guru on social media.
In a church context, 'Papst' (pope) is often used with certain verbs. Typical combinations are 'zum Papst gewählt werden' (to be elected pope) or 'eine Audienz beim Papst haben' (to have an audience with the pope).
Nach langer Diskussion wurde ein neuer Papst gewählt.
After a long discussion, a new pope was elected.
expert
'der Experte' and 'der Papst' can both refer to a person who knows a great deal about a field. 'Experte' is the normal and neutral word for a knowledgeable specialist. In this relation, 'Papst' does not mean the religious leader, but is used figuratively: someone is considered an especially great authority in a field. This sounds stronger and often somewhat humorous or admiring. In everyday use, 'Experte' is usually safer and more neutral; 'Papst' fits better when you want to emphasize that someone is considered an absolute top authority.

Mein Bruder nennt diesen Koch den Pizza-Papst der Stadt.
My brother calls this chef the pizza pope of the city.
Für die Reparatur fragen wir lieber einen Experten.
For the repair, we would rather ask an expert.