The son of music legend Willie Nelson was approached early on by Cooper to consult on the film's music, but quickly transitioned into a songwriting role as well. Nelson's hand is visible in the majority of the film's songs, co-writing with Cooper and Gaga on most of them. As it turns out, his role wasn't limited to just writing behind the scenes: Nelson and his real-life band, Promise of the Real, appear onscreen as the band performing with Cooper's character Jackson. You'll notice Lukas as the guitarist throughout the film.