Julian Bashir was a Terran slave who joined the Terran Rebellion against the Klingon-Cardassian Alliance in the 2370s, soon rising to the rank of captain. An angry and impetuous individual, Bashir didn't get along well with anyone.
In 2371, Bashir proposed that the rebels destroy Terok Nor in order to prevent Jennifer Sisko from completing a transpectral sensor array which would reveal the rebels' hiding places in the Badlands. Bashir was surprised when Benjamin Sisko returned from the dead; he immediately got into an argument with Sisko who promptly decked him. (DS9: "Through the Looking Glass" )
When Sisko's counterpart from the mirror universe visited Terok Nor in 2372 to help the rebels complete construction of the warship ISS Defiant, Bashir immediately hit Sisko as payback for getting punched the previous year which he claimed was delivered by that Sisko.
Bashir and Jadzia Dax were lovers; when the Alliance attack on the rebel-occupied Terok Nor was imminent, he and Jadzia took a raider and managed to delay the Alliance's assault by projecting a series of warp shadows to draw off the enemy fleet. After this successful diversion, Bashir returned just in the nick of time to help the Defiant finish off the Regent's flagship at the Battle of Terok Nor. Smiley O'Brien was less than pleased at being grateful for Bashir's timely return. (DS9: "Shattered Mirror" )
When his lover Jadzia was killed during a skirmish with the Alliance in early 2375, Bashir became even more irritable and unreasonable. He personally shot and killed Vic Fontaine and wanted to torture Ezri Tigan. (DS9: "The Emperor's New Cloak" )