Ambassador

For player characters
For player characters, "Ambassador" is a title obtained by gaining exalted reputation with all six home cities of your faction:
 * For the Alliance: Stormwind, Ironforge, Darnassus, Gnomeregan, Exodar and Gilneas
 * For the Horde Orgrimmar, Thunder Bluff, Undercity, Darkspear Trolls, Silvermoon and Bilgewater Cartel

The title precedes the player's name, in the following format:
 * Ambassador 

For mobs and NPCs
Some mobs and NPCs, will have their name or title composed of either "Ambassador", "Emissary", "Envoy" or "Speaker" which usually means they are diplomats from a faction or organization to some other faction or organization.