Who is Las Zenow and Tryma Arcanio from Forward the Foundation and what is their importance?

Las Zenow and Tryma Arcanio are successive Chief Librarians of the Galactic Library during the final phase of Hari Seldon's life, Zenow has a gray beard turning to white. He cooperates with Hari in locating an appropriate world on which to establish a Foundation to preserve human knowledge by publishing the Encyclopedia Galactica. Zenow wishes that he were young enough to participate. Frustrated by opposition by Librarian Gennaro Mummery, Zenow retires to his home planet Wencory and is succeeded by Tryma Arcano, also a progressive but more popular with the Library Board.