What Lyricist is known for collaborations on musicals such as "Rex" and "Fiddler on the Roof"? 
Rex (musical): Rex is a musical with music by Richard Rodgers, lyrics by Sheldon Harnick and libretto by Sherman Yellen, based on the life of King Henry VIII. Sheldon Harnick: Sheldon Harnick (born April 30, 1924) is an American lyricist best known for his collaborations with composer Jerry Bock on musicals such as "Fiddler on the Roof".
Sheldon Harnick