Which House M.D. character is known by the number 13?

Remy Hadley is the House M.D. character known by the number 13.

Remy Hadley, played by Olivia Wilde, joins House's diagnostic team during the fourth season. House calls her “Thirteen,” a nickname based on her number in the competition used to select new members of his team.

The character's full name is Remy Beauregard Hadley. She is a physician whose medical history becomes an important part of the series, especially after she learns that she carries the gene associated with Huntington's disease. That storyline explores uncertainty, testing, relationships, and the possibility of future illness.

“Thirteen” is a character nickname, not the name of a separate doctor. Several other fellows compete for positions in the same storyline, which can cause confusion when identifying her. Olivia Wilde played Hadley for much of the series, and the number became the character's best-known identifier.