DIED. JESS THOMAS, 66, tenor; from a heart attack; in San Francisco. At 6 ft. 3 in. with a solid, profoundly expressive tenor, Thomas was truly a born Wagnerian hero. Raised in South Dakota and a student of child psychology before devoting himself to a musical career, he debuted at the Metropolitan Opera in 1962 as Walther in Die Meistersinger. With a repertoire encompassing virtually every heldentenor role composed by Wagner, Thomas went on to become that rarity of the '60s and '70s -- a singer whose vocal and dramatic power could match that of the great heroic soprano of the era, Birgit Nilsson.