In Star Trek Online, there are many characters. There are two types like most MMO's, they're NPCs and playable characters. Some of the NPCs give you missions to increase your skill level. Some Npc's sell goods that could be essential for you to progress in the game. Some NPCs will give you missions for your duty officers to perform. Note: You cannot do these missions unless you have duty officers suited for those missions. Some NPCs are part of your missions that you may have to help or destroy depending on the mission. Some Npc's give you information on certain content. And other Npc's serve no purpose. Some NPCs give you items if there is a promotional event going on. The playable characters are characters you play as. They include several races from the Federation, Klingon Empire and Romulan Republic. You can interact with other characters, everything from chatting to PVP.