One of the most important fixtures in American music during the second half of the twentieth century was Leonard Bernstein. A celebrated conductor and composer, Bernstein also shared his passion for music as an educator through his Harvard lectures, his Omnibus television program, and his series of Young People's Concerts for CBS.
Bernstein was the longtime conductor of the New York Philharmonic Orchestra and is probably best known as the composer of the musicals On The Town and West Side Story and the operetta Candide. He also composed the film score for On the Waterfront. Through his many apperances on television spanning decades, Bernstein was an enthusiastic teacher of music, inspiring many throughout the world with his knowledge of and passion for the music he presented.
Below is one of my favorite Bernstein songs, the finale "Make Our Garden Grow" from Candide. This version is from a tribute done for his 70th birthday, sung by Jerry Hadley and Dawn Upshaw and conducted by Seiji Ozawa.
Postscript: Of course, his name is also among the few lyrics most people understand/remember from any verse of R.E.M.'s "It's The End Of The World As We Know It (And I Feel Fine)" and is usually yelled if singing along with others.