Stephen Damian O'Neill (born 15 January 1961) is the lead guitarist in the pop-punk band, The Undertones.

O'Neill wrote several album tracks and singles during the career of The Undertones, usually writing with bassist Michael Bradley.

In 2001, O'Neill released the experimental electronic album A Quiet Revolution on Alan McGee's Poptones label.

Furthermore, he as X-Valdez (nom de plume) released a 12-inch "Higher Grace" with arrangements by Xavier Jamaux and Athena Constantine on vocals on Toy's Factory in 2000.

[2][3] Since 2012, Damian O'Neill and three of his former bandmates of That Petrol Emotion, Raymond Gorman, Ciaran McLaughlin and Brendan Kelly are active as London-based The Everlasting Yeah,[4] playing kosmische Krautrock influenced music mixed with most individual soundscapes creating sheer amazing atmospheres with powerful guitary, percussionized tunes.