Jaques is listed in the cast of characters as one of the "lords attending on Duke Senior." He is one of the loyal lords who followed Duke Senior into exile in the Forest of Arden. Jaques is sometimes referred to as "the melancholy Jaques" because he is typically sad, expresses a pessimistic philosophy, and spends most of his time alone because he doesn't like most people. Allthough he is always sad, he is usually funny. He is noted for his speech about the "Seven Ages of Man," which begins with
All the world's a stage,
And all the men and women merely players
This famous speech is to be found in Act 2, Scene 7.
eNotes contains a great deal of information about Jaques (pronounced jay-queez) which you can access by clicking on the links below and looking elsewhere in the Study Guide for Shakespeare's As You Like It.