Doctor Terence Epstein was a Starfleet cybernetics expert in the 24th century. Beverly Crusher was one of his fans, and Epstein once spoke at her medical school.
In 2364, he was stationed at Starbase 74. While there, Crusher hoped to consult him regarding her proposals for combining cybernetics with medical regeneration. (TNG: "11001001")
A small scene in the script but not in the episode called for Epstein to appear on screen, and established him as being only twenty-six years old.