Optio Miles O'Brien in 2376.
In the alternate timeline where Khan Noonien Singh won the Eugenics Wars, an Optio is an executive officer's position held by an Augment in the Earthfleet of the Children of Khan. It is roughly equivalent to a Lieutenant Commander or Commander in Starfleet. An Optio can usually be found serving as a first officer under the command of a Princeps.
This timeline's version of Miles O'Brien was an Optio, and served on the warship Defiance under Princeps Julian Bashir. (ST - Myriad Universes novella: Seeds of Dissent)