Simplify the following text for a Grade 9 native English-speaking person.
Original: Bobby Darin ( May 14 , 1936 â `` December 20 , 1973 ) , born Walden Robert Perciville Cassotto , was an American singer , actor and accomplished musician .
Simplified: Walden Robert Cassotto ( May 14 , 1936 â `` December 20 , 1973 ) , better known as Bobby Darin , was an American pop singer , most famous during the 1950s .