Zoë Alleyne is a 'Browncoat', having served with distinction under Mal's command in the war. Now, she's the most trusted member of his crew, Serenity's unflappable second-in-command. A straight shooter in both combat and conversation, Zoë's opinion is every bit as valued as her more violent skills. She's fiercely loyal to Mal, and would -- and on occassion has -- followed her Captain to hell and back. That said, her ultimate allegiance lies with another -- Zoë is married to Wash, Serenity's pilot. - From The Official Serenity Website
Behind the Scenes
According to Serenity: The Official Visual Companion, by Joss Whedon, Zoë's last name at the time of the War of Unification was Alleyne and is Washburne at the time of the series.