Miles O'Brien (alternates)

Alternate timelines and realities
In an anti-time past created by Q, O'Brien was surprised in 2364 that Captain Jean-Luc Picard was aware that he had built model ships in bottles as a child. Unbeknownst to O'Brien, the captain had travelled back in time from 2370. Picard had learned of his interest in model ships from a conversation in 2366. 

In an alternate timeline created by the USS Defiant being sent back in time to the 22nd century, the ship's crew, including O'Brien, settled on Gaia IV. He married Rita Tannenbaum ten years after the Defiant's crash and was the last member of the crew to give up hope about returning to the 24th century. Their descendants included Miranda O'Brien and their great-great-great-great-great-granddaughter Molly. The name "Molly" had been passed down through the O'Brien family for 200 years. 

In another alternate timeline in which the Cardassian Union did not withdraw from Bajor in 2369, Chief O'Brien received a commission as a lieutenant when he became the chief engineer of the USS Enterprise (NCC-1701-E) in 2373 after Lieutenant Commander La Forge transferred to the USS Sugihara. He was killed six months later when the Enterprise was destroyed in the Bajor system by a Dominion ship commanded by Omet'iklan. 

In an alternate reality in which the Borg emerged victorious from the Battle of Wolf 359 in 2367, O'Brien still served aboard the Enterprise-D. Like his primary universe counterpart, this O'Brien was married to Keiko O'Brien and had a daughter, Molly, though they were killed in a Borg attack. 

When the crew of his Enterprise-D encountered the crew of the Enterprise-D of the primary universe, this O'Brien knocked out his counterpart and unsuccessfully attempted to take his place. 

In another alternate reality, Federation and Dominion delegations met on Deep Space 9 to negotiate a treaty in response to the Dominion's peace overtures in 2371. However, during the talks, Odo was murdered with a phaser. Consequently, the negotiations broke down and the Dominion launched an attack on DS9. Both his wife Keiko and his daughter Molly were killed during the attack, leaving O'Brien devastated. Although the Federation forces were eventually able to push the Jem'Hadar back through the Bajoran wormhole, the Dominion was able to capture Commander Benjamin Sisko, Major Kira Nerys and Doctor Julian Bashir.

He assisted the Trill diplomat Curzon Dax in modifying the USS Defiant to travel to alternate realities. Curzon then began to search the multiverse for another version of Odo. Curzon's plan was to return to his own reality with this other Odo, who would claim that he had faked his own death in order to expose the traitor aboard DS9. After arriving in the primary universe, Curzon attempted to recruit Odo for that purpose but Commander Sisko believed that interfering in the affairs of another universe would violate the Prime Directive. Refusing to take "no" for an answer, Curzon kidnapped Odo while he was regenerating, commandeered the Defiant of the primary universe and returned to his own reality. In accordance with Curzon's plan, Odo assumed the identity of his murdered counterpart. Besides Curzon, O'Brien was the only person aboard DS9 who was aware that this Odo was from an alternate reality. 

Kelvin timeline
In an alternate reality created by Q, O'Brien was the first officer under his wife, Captain Keiko on board the USS Defiant (alternate reality NX-74205). He then rescued Sisko, Captain Kirk and his party after Changelings had murdered Chancellor Worf using a shuttle. O'Brien was then assisted by Commander Scott in fixing the warp drive. The two then discussed engineering.