This is the 12680th most frequent Russian word.
королем
"Королем" means "king" (instrumental case) in English.
The word 'королем' is in the instrumental case, denoting the role or status acquired.
Он стал королем по воле народа.
He became king by the will of the people.
Here, 'королем' refers to a chess piece and is in the instrumental case, describing the means of his action.
Играя королем, он всегда побеждал в шахматах.
Playing with the king, he always won in chess.
The use of 'королем' in this case also denotes the role or title, provided instrumentally to indicate respect or honorific designation.