Simplify the following text for a Grade 6 native English-speaking person.
Original: Marie Dionne Warwick ( born December 12 , 1940 ) is an American singer and actress who became a United Nations Global Ambassador for the Food and Agriculture Organization , and a United States Ambassador of Health .
Simplified: Dionne Warwick ( December 12 , 1940 ) is a well known American R&B singer .