Use jovial to describe people who show good humor and are full of joy. Santa Claus, with his constant "ho-ho-hoing" is a jovial figure.
Jocose and jocular are similar words, but they refer more to things that actually cause laughter. Jovial is derived from the Late Latin Iovialis, "relating to Jupiter" — the ancient Roman god of the sky. In astrology, people born under the sign of Jupiter are said to be joyful.