Wayne's version of the singing cowboy was much darker than the later ones. He appeared in Riders of Destiny (1933), walking purposefully toward a showdown in his black instead of white hat. He sang about "streets running with blood" and "you'll be drinking your drinks with the dead".

Wayne's image of a singing cowboy was unique and memorable, but, anyway, he didn't continue working with the singing cowboy format. Wayne just wasn't able to sing! As his singing was dubbed, it didn't sound similar to his own speaking voice, which was one of the actor's unique peculiarities. So, due to that, Wayne refused to renew his contract.

More Info: en.wikipedia.org