Reinier de Ridder, also known by his initials RdR, is a Dutch professional mixed martial artist. He currently competes in the Light Heavyweight division of the Ultimate Fighting Championship (UFC). He previously competed in ONE Championship, where he is a former ONE Middleweight World Champion and ONE Light Heavyweight World Champion. De Ridder was the third two-division champion in ONE history, having previously held the middleweight and light heavyweight belts simultaneously. As of August 22, 2026, he is #9 in the Meta UFC light heavyweight rankings.