Haruhi Suzumiya is the title character and leader of the SOS Brigade , whose energetic and eccentric character proves to be the driving force for the series. She has a mind for adventure which often leads her subordinates to be swept into her plans. Haruhi cannot stand boredom so she comes up with various activities for the SOS Brigade, making them participate whether they like it or not.

While being smart, beautiful and energetic, Haruhi was eyed as an oddball ever since middle school. What Haruhi does not know is that she has an outstanding power to change the environment around her as she pleases, and by subconsciously using it she gathers Mikuru Asahina, Itsuki Koizumi, and Yuki Nagato into one place, the SOS Brigade.

Source:Wikipedia