A king or monarch; a supreme ruler. Also used figuratively for someone who dominates a field.
中世の記録にはその地を治めた王者の名が残っている。
Medieval records preserve the name of the ruler who governed that land.
彼はロック界の王者と呼ばれている。
He is called the king of the rock world.
王者の風格を感じさせる振る舞いだった。
His behavior conveyed the bearing of a ruler.
A champion — someone who wins competitions or a person/team that consistently shows superior ability.
昨年の大会の王者が今年も防衛に成功した。
Last year's champion successfully defended the title again this year.
王者が敗れて会場はどよめいた。
The crowd gasped when the champion was defeated.