Nat King Cole was an American jazz singer and musician who rose to fame in the 1940s and 1950s. He was known as the 'King of Crooners' for his smooth, velvety singing voice. He was one of the first African-American performers to gain widespread acceptance in the mainstream music industry. He had a string of hits including 'UNFORGETTABLE', 'Mona Lisa', and 'Nature Boy'. He was also a successful songwriter and pianist.