Q. This question came up in a shiur this week and I would like to know Rav Miller’s opinion. Who was the happiest person in Tanach?

A. It would seem from the Talmud and Midrashim that at least for a short time, Adam was the happiest human being ever.
Horav Shlomo Miller Shlit’a suggested that King Yosam ben Uziyahu is a good candidate. The Talmud (Suka 45b) teaches that if the merits of Yosam were added on to those of Rabbi Shimon bar Yochai and his son they could save the world from the time of its creation until the end of time. Rashi (ad loc.) explains: “Yosam ben Uziyahu was a righteous man, who was more humble and modest than other kings. He merited to show honor to his father, and for this reason, the pasuk “a son shall honor his father” (Malachi 1: 6) was said on him, and his merits were unsurpassed.
Although Maharsho (ad loc.) mentions that like Rabi Shimon bar Yochai and his son Elazar, Yosam suffered great physical pain in his lifetime, he possessed great emunah, trust in Hashem and love to Him, and therefore lived a very happy and joyous life.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a.