Miles O'Brien (mirror)

In the main mirror universe continuity, Miles "Smiley" O'Brien was a $𝜇$ slave of the Klingon-Cardassian Alliance with a theta designation until 2370. With the death of Benjamin Sisko a year later, he became leader of the Terran Rebellion. When Sisko first met O'Brien, O'Brien's serious demeanor was so noticeable that Sisko decided to designate O'Brien as "Smiley", a name that stuck thereafter.

In 2370, he was working in the ore processing facility on $𝜇$ when he encountered the primary universe Julian Bashir. He and Sisko later helped Bashir and primary universe Kira Nerys escape from the station, and the clutches of Intendant $𝜇$. 

In 2371, O'Brien visited the primary universe and abducted its version of Benjamin Sisko, bringing him back to the mirror universe. There, the two men persuaded Professor $𝜇$ to abandon her work on a transpectral sensor array. Jennifer did so, and even joined the Rebellion. 

Whilst O'Brien was in the primary universe, he secretly downloaded numerous computer files from Deep Space 9's computer system, including complete plans for USS Defiant (NX-74205) (I). 

In early 2372, O'Brien was among the rebels who commandeered Terok Nor from the Alliance and imprisoned Intendant Kira. Having by this time constructed their own $𝜇$, they were disappointed when they discovered it had significant technical faults that prevented it becoming operational. O'Brien once again worked with the primary-Sisko, correcting the Defiant's faults and successfully repelling an attack led by Regent $𝜇$. 

In 2375, when Quark and Rom came to the mirror universe with a Klingon-built cloaking device, they were able to escape Terok Nor with the aid of $𝜇$ and $𝜇$. Smiley and his rebels pursued in the Defiant and found the cloaking device had sabotages the systems on Regent Worf's ship; the Regency 1, and captured both, scoring a massive victory over the Alliance. 

O'Brien, now a general, began to lose favor with the Rebellion in the face of the growing power of fellow Generals' $𝜇$ and Bashir. This began when Bashir openly challenged O'Brien's position after allowing Quark and Rom to return to their universe with the cloaking device, which the Rebels could have kept for themselves (despite the fact that the Rebellion had now developed cloaking technology of their own). The situation worsened when he was thought to be going "soft" after starting a romantic relationship with his second-in-command; Commander $𝜇$. O'Brien was effectively ousted as leader of the Rebellion when he openly ordered the new $𝜇$ shipyard shutdown as it was believed to be to easy a target. However, Zek and Bashir planned an attack on $𝜇$ and $𝜇$ and used it sway most Rebel leaders to follow them to the shipyard and use the newly-constructed warships they had made there. Smiley, tipped off (anonymously) by Intendant $𝜇$, alerted Zek and Bashir about an imminent attack on the shipyard but failed to persuade them to turn back. Empok Nor was destroyed along with the warships, most of the Rebels stationed there killed and Zek and Bashir were captured. Smiley initially began to lose hope, but Keiko and his right-hand man; General $𝜇$, convinced him to rally his troops and continue to lead them to the coming victory over the Alliance. 

After the crippling defeat at the shipyard; the rebellion fell back to Terok Nor where they consolidated their forces and fortified their positions. It was with the help of Ilayna Ghemor who was the emissary of the Prophets that the station was fortified with weapons and artillery to help deal with a forthcoming Alliance attack. Subsubquent events lead to the station's destruction and the rebel fleet being on the run once again. O'Brien and the fleet went into hiding in the badlands. Though O'Brien did not know it, his lover, $𝜇$ was an operative of Memory Omega and worked to bring the rebel fleet together with her organization's own fleet and the forces of Mackenzie Calhoun. Keiko managed to convince Miles to attend a meeting with Calhoun. The first meetings did not go well with nethier leader giving up power and refusing to work together. Subsequent events saw Miles learn about Memory Omega and Keiko's role as one their agents. This, in turn, lead to a strain on their relationship. After a short estrangement, however, the two resumed their relationship. The rebel fleet was drafted into the combined fleet and proceeded to participate in several significant battles.

During the final push to end the war, Miles lost several comrades with whom he had fought for years. Amongst these losses, was his first officer on the Defiant Leeta who was the wife of Ezri Tigan. Miles recruited Ezri to be his new first officer, a position that she accepted. While at a meeting of rebel leaders on Bajor, Miles also voiced his disapproval of the proposed genocide of the Cardassian race in order to cripple their ability to continue the war.

After the war ended, Miles continued serving in the fleet for a brief period of time. One of his last duties was to visit Worf in prison and released him because the war ended. During their brief meeting, Miles allowed Worf to commit sucide with his own dagger rather then face a life of dishonor. Miles and Keiko married and Miles retired from active service as an officer. Miles and wife returned to Earth and settled in Ireland. Miles started a farm and was content to live a quiet life. While working on his newly established farm, Miles was visited by Saavik. Saavik gently probed Miles reasons for not participating in the new government of the Galactic Commonwealth; complimenting his leadership abilites as she did so, stating that good leaders were always needed. In the end, however, Saavik understood Miles choice and each wished the other well and parted ways. 

Dark Mirror continuity
In the Dark Mirror continuity where the Terran Empire survived in to the 24th century, Miles O'Brien served as conn officer aboard the ISS, from 2364 until at least 2367. 

Dark Passions continuity
In the Dark Passions continuity, Miles "Smiley" O'Brien was a Terran slave of the Klingon-Cardassian Alliance with a theta designation until 2370. With the death of Benjamin Sisko a year later, he became leader of the Terran Rebellion.

When Sisko first met O'Brien in 2369, O'Brien's serious demeanor was so noticeable that Sisko decided to designate O'Brien as "Smiley", a name that stuck thereafter. It was shortly after this that Sisko and O'Brien met $𝜇$, when she went to $𝜇$'s shuttlebay searching for $𝜇$. Jadzia found Hansen, but was ignored, so Jadzia joined the Rebellion and told them what she knew of Hansen. 

Star Trek Online continuity
Miles and Keiko were the parents of James O'Brien, who later became a captain in the restored Terran Imperial Starfleet. James later murdered Miles, becoming the leader of the Terran Empire.