Bruce has been on the run for months because Thaddeus 'Thunderbolt' Ross wants Bruce because he is hulk so he gets the Leader to make the Abomination. While on the run he deals with depression which does not go well with Dissociative Identity Disorder we find out why this is a thing through this movie because Bruce was abused as a child, This creates Joe Fixit is a manifestation of his teenaged angst; mean and smart and calculating, and wanting to project a somewhat juvenile "tough guy" persona upon the world. Bruce/Hulk has to defeat Joe/Savage Hulk in his mind
