Oskar Eustis, the associate artistic director at the Mark Taper Forum, will become the new artistic director at Trinity Repertory Company in Rhode Island.He replaces Richard Jenkins,who left to resume a full-time acting career. Eustis came to the Taper in 1989 as a resident director in charge of new play development. Prior to that, he had been artistic director at the Eureka Theatre in San Francisco, a small company that had received critical acclaim but fell victim to financial hardship. While at the Eureka, Eustis had commissioned a young playwright, Tony Kushner , to write an epic about AIDS. The commission became “Angels in America,” the first half of which, “Millennium Approaches,” won a 1993 Pulitzer Prize. When Eustis made the move to the Taper, he, in essence, brought “Angels” with him. The play opened at the Taper nearly two years ago under Eustis’ direction and subsequently made the move to Broadway. George C. Wolfe directed it on Broadway, where it is still running (at the Walter Kerr). While Eustis concentrated most of his efforts on new development while at the Taper, working on the theater’s yearly new works festival, he also recently directed a mainstage revival of “Julius Caesar.” He is due to assume the artistic reins at Trinity Rep in June.