Miles Edward O'Brien is a character in the Star Trek franchise, portrayed by actor Colm Meaney. O'Brien appears occasionally in all seven seasons of Star Trek: The Next Generation and is a main cast member of Star Trek: Deep Space Nine. O'Brien was originally the transporter chief of the USS Enterprise-D. He was later promoted to chief of operations of Deep Space Nine. Being portrayed in 225 episodes overall, O'Brien is the Star Trek character with the second most appearances in the Star Trek franchise, second only to Worf (Michael Dorn). O'Brien is the only major Star Trek character described as both ethnically Irish and born in Ireland; Colm Meaney, the actor who portrays him, is Irish. O'Brien is also the only regular cast member in Star Trek to be a non-commissioned officer. Source: Wikipedia (en)