Upon his return, King Tiridates III imprisoned Gregory in a pit on the Ararat Plain for twelve to fourteen years. (Tiridates’ father, King Khosrov II, was the king Gregory’s father tried to assassinate.) But Gregory was released so that he could attend the king and help restore the King’s sanity after Tiridates had been betrayed by the Roman emperor Diocletian. (Diocletian had conquered large portions of the western provinces of Armenia.)
In 301, Gregory baptized Tiridates and members of the royal court, and the king enjoined Gregory to convert the entire nation. Gregory became the first Catholicos (basically a Patriarch, the equivalent of the pope) of the Armenian Apostolic Church, and Armenia became the first country to adopt Christianity as its state religion.
Gregory’s feast day is March 23.