Hayate is one of Lisa's attendants. While he only makes a handful of appearances in the manga, Hayate in the anime forms a strong rivalry/friendship with Tomoka, and the two occasionally battle one another in friendly duels. Hayate is a very calm, loyal, and serious individual who will go to great lengths for his mistress, Lisa; this usually involves doing some sort of research or private investigating. Tomoka nicknames him "ninja" because of his stealthy ways, only revealing himself when attending to Lisa, or to attack.

(Source: Wikipedia)