Who is Leontes in Shakespeare's The Winter's Tale?

King Leontes of Sicily is the central character in The Winter’s Tale. In the play’s first half, an irrational jealousy possesses the king. He accuses his wife Hermione of having an affair with his best friend, King Polixenes of Bohemia. No one can convince Leontes of their innocence, and he goes so far as to plot the death of his friend and his wife’s newborn child. He forces Hermione to stand trial in court immediately after she gives birth in prison.
Leontes’s seeming madness results in the deaths of several people. His son Mamillius dies, supposedly of grief over being separated from his mother. When Antigonus agrees to abandon Hermione’s child in a remote location, he is eaten by a bear and the men on the ship drown in a storm. Leontes loses his son, his friend (who escapes back to Bohemia), his daughter, and his wife, whom the noblewoman Paulina reports as dead following her collapse.
The second half sees a repentant Leontes. Sixteen years have passed, and Leontes grieves daily, thinking of Hermione and his children:

Whilst I rememberHer and her virtues, I cannot forgetMy blemishes in them, and so still think ofThe wrong I did myself; which was so much,That heirless it hath made my kingdom andDestroy'd the sweet'st companion that e'er manBred his hopes out of.

These griefs have made Leontes a kinder person. When his daughter Perdita, who was found and raised by shepherds, escapes to Sicily with Polixenes’s son Florizel, Leontes welcomes them with open arms. He even reconciles with Polixenes. Because of this change in behavior, Paulina reveals, in the guise of a statue, that Hermione is still alive. Just as the play moves from winter to spring and tragedy to comedy, Leontes transforms from an angry and jealous husband into a compassionate father and friend.
http://shakespeare.mit.edu/winters_tale/full.html