A king, ruler, sovereign, or monarch — the person who rules a country or territory.
中世の王は城に住み、国を治めていた。
Medieval kings lived in castles and ruled their countries.
その国の王が即位式で祝辞を述べた。
The country's king gave a speech at the coronation.
チェスでも将棋でも、王を守ることが最優先だ。
In both chess and shogi, protecting the king is the top priority.
Figuratively, 'king' is used as a title or suffix to indicate someone preeminent in a field (tycoon, champion, master).
彼はセールスの王と呼ばれるほど成績がいい。
He performs so well he's called the king of sales.
その選手はスプリントの王として知られている。
That athlete is known as the sprint king.
In shogi, refers to the king piece of the players (the word used for the king piece).
王が詰まされるとその局は終わる。
When the king is checkmated, the game ends.