Niles on The Voice is Niall Horan, an Irish singer-songwriter and former member of the boy band One Direction. He became a coach on The Voice starting from Season 23 and has won the competition twice with his teams in Seasons 23 and 24. He is known for his expertise as an international pop star and his successful solo career, which makes him a valuable mentor to contestants on the show.
To clarify, Niles is not a contestant or a character but rather tied to Niall Horan, who serves as a coach on The Voice.
