Koizumi Itsuki

Age: 16-17
Occupation: Esper, Vice Commander,Student (Grade 11)

is the fifth person to join the SOS Brigade, recruited by Suzumiya Haruhi because he fit with her idea of a "mysterious transfer student", after he was transferred into North High. He later reveals himself to Kyon as an esper, working for a group he only acknowledges as the 'Agency' (translated as The 'Organization' in the anime). Though he was sent to North High by the 'Agency' to observe Suzumiya Haruhi, he believes that it was her will that really brought him there.

he has a polite manner and likes to go into long lectures and explanations with very expressive hand gestures.

In the light novels, he's described at being very bad at board games and cards, but in the anime it's Kyon who usually loses to him