Thomas Francis Dorsey Jr. was an American jazz trombonist, composer, conductor and bandleader of the big band era. He was known as the "Sentimental Gentleman of Swing" because of his smooth-toned trombone playing. His theme song was "I'm Getting Sentimental Over You". His technical skill on the trombone gave him renown among other musicians. He was the younger brother of bandleader Jimmy Dorsey. After Dorsey broke with his brother in the mid-1930s, he led an extremely successful band from the late 1930s into the 1950s. He is best remembered for standards such as "Opus One", "This Love of Mine" featuring Frank Sinatra on vocals, "Song of India", "Marie", "On Treasure Island", and his biggest hit single, "I'll Never Smile Again".