Miles Edward O'Brien enjoys kayaking, poker, and darts. He got married to Keiko on the Enterprise-D on stardate 44390 (in year 2367, "Data's Day"). He had a daughter Molly in TNG's season five (in year 2368, stardate 45156, "Disaster") and a son on DS9 (in year 2373, stardate ~50450, "The Begotten").

He was a tactical officer on one of his previous assignments. He transferred to Deep Space Nine station along with his family. He's sorry to leave the Enterprise, but pleased at the promotion (to Master Chief of Operations).

He saw the Cardassians commit unspeakable atrocities and lost a close friend at the massacre at Setlik III. The war changed and hardened him. The first man he ever killed was a Cardassian who jumped him on patrol. As he tells the story to another Cardassian in the TNG episode, The Wounded, "I never killed anything before. When I was a kid I would worry about having to swat a mosquito. It's not you I hate, Cardassian: I hate what I became because of you."

Colm Meaney had decided that he would like to switch shows.

Keiko will not deal well with the change of scenery and following her husband to this hellhole in order to support his career. Look of more domestic strife. He would receive a commission and would be "Chief Operating Officer" in this case.

O'Brien died on stardate ~48600 (in year 2371), and he is replaced with an almost identical himself from an alternate timeline ("Visionary").