Star Trek: 10 Things You Didn't Know About Miles O'Brien
2. He's All Smiles That One
Miles 'Smiley' O'Brien made his first appearance in Crossover, where he was a brow-beaten Terran slave, favoured by the Intendent and by Ben Sisko. A chance meeting with the Prime Universe version of Dr. Bashir inspires him to stage a break-out, eventually escaping the station and rising through the ranks.
His next appearance in Through The Looking Glass sees him pull a disrupter on the Prime Universe version of Sisko, capturing him and bringing him over to the Mirror Universe. Colm Meaney described this version of O'Brien as a 'dirtier, scuzzier' version of the character, though hastened to add that it was due to the life that Smiley had led.
The Star Trek: Mirror Universe novels feature O'Brien marrying Keiko, just like their Prime Universe counterparts. In those stories, the O'Briens retire from the resistance and move to the island of Inis Mór, one of the Aran Islands off the west coast of Galway.