

From Wikipedia, the free encyclopedia. Michael O'Neill (born May 29, 1951) is an American actor. With a career stretching through three decades, he usually portrays senior law enforcement or military officers. He is perhaps best known for his role as Special agent Ron Butterfield, the head of President Josiah Bartlet's Secret Service detail, on The West Wing. He played CTU Administrative Director Richard Walsh in the first two episodes of 24. He played Sgt. Maj. Ron Cheals in the CBS action-drama series The Unit. He starred in the Season Six 2 part Finale of Grey's Anatomy as the broken widower who holds the hospital hostage with a 9mm while pursuing the doctors responsible for unplugging his wife. His most notable film performances occur in Seabiscuit, Secondhand Lions, Transformers, Dancer, Texas…
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Grey's Anatomy
2005 • TV
Gary Clark

NCIS
2003 • TV
Riley McCallister

Criminal Minds
2005 • TV
Det. Yarbough

The Mentalist
2008 • TV
Sheriff Nelson

Tracker
2024 • TV
Buck Avery

S.W.A.T.
2017 • TV
Carl Luca

CSI: Miami
2002 • TV
Jerry Blackburn

Prison Break
2005 • TV
Herb Stanton

24
2001 • TV
Richard Walsh

NCIS: Los Angeles
2009 • TV
Ret. U.S. Army General Richard Collins
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