Thirteen, of course, is not the real name of this character. However, it's what everyone now refers to Remy Hadley as because it was the number assigned to her during season four, when House used a Survivor-type game to choose his next team members.
A couple interesting facts about Thirteen: she has Huntington's disease; and she's a bisexual.
Near the end of season five, though, she began a relationship with Foreman.
Dr. Cameron: What did Cuddy want?
House: I kinda hit that last night, so now she's all on my jock.
Thirteen: Wow, she looks pretty good for someone on roofies.
Thirteen: Retinal vein occlusion was fixed. Her doctor said it was a venous anomaly
House: Is he in this room? Because if he's not, I don't care what he thinks. Unless he's a she and she was there last night too, in which case I care very deeply.