Daniel or Dan O'Brien may refer to: Daniel O'Brien, 1st Viscount Clare (1577–1663), MP for County Clare, younger son of Connor O'Brien, 3rd Earl of Thomond Daniel O'Brien, 3rd Viscount Clare (fl. 1670–1691), son of Connor O'Brien, 2nd Viscount Clare Daniel O'Brien, 4th Viscount Clare (died 1693), son of Daniel O'Brien, 3rd Viscount Clare Daniel O'Brien (comedian) (born 1986), American humorist, writer and comedian Daniel Pitt O'Brien (1900–1957), Secretary of State of West Virginia Dan O'Brien (born 1966), American decathlete Dan O'Brien (author) (born 1947), American author and rancher Dan O'Brien (baseball coach) (born 1971), American college baseball coach Dan O'Brien (baseball executive), former general manager of Major League Baseball's Cincinnati Reds Dan O'Brien (footballer) (1884–1917), Australian rules football player Dan O'Brien (pitcher) (born 1954), American baseball player Dan O'Brien (playwright) (born 1974), American playwright Dan O'Brien (soccer) (born 1986), American soccer player Dan O'Brien (sports journalist), American sports journalist, author and screenwriter Dan O'Brien Sr. (1929–2017), former front office executive in Major League and minor league baseball Dan O'Brien (American football) (born 1963), American college football coach and administrator Danny O'Brien (gridiron football) (born 1990), American college football quarterback Danny O'Brien (journalist) (born 1969), British technology journalist