The two personalities of the schizophrenic Hancock (2008) prevent the film from being better than it is. But they don't prevent it from being entertaining, and from having at least some substance. One personality focuses on Will Smith, an alcoholic vagrant who also happens to have super powers. He can stop speeding trains, prevent bank robberies, foil disasters, but he's usually drunk when he does so, and as a result often leaves a wake of destruction behind. He's wanted for numerous crimes by local law enforcement. Hancock hates being a super hero. When he saves an idealistic publicist named Ray Embrey (Jason Bateman) from being run over by a speeding locomotive, the publicist offers to help him change his image. This involves getting a spiffy costume, accepting a prison sentence for his misdeeds, thanking the local police for their good work, and not wreaking havoc. Hancock actually wants a better public image, and when the publicist's advice begins to pay off, he is happy.
What makes Hancock an interesting character is Will Smith's acting. Smith brings the character to life as a real individual rather than as a flat comic book stereotype. Hancock has a genuine personality, and he's more recognizable as an individual than most other cinematic superheroes.
Of course, there has to be an explanation for Hancock—where did he come from, where did he get his powers? All he can remember is waking up in a Miami hospital some eighty years before—with amnesia and super powers.
Here's where the film's second personality comes in. It turns out that when the publicist takes Hancock home for dinner and introduces his wife, Mary (Charlize Theron), strange things happen. She behaves in a cold and hostile manner towards Hancock. When they are alone in the kitchen, they're drawn to each other. They find themselves embracing. Suddenly, she throws Hancock through the kitchen wall. She too has super powers, unbeknownst to her husband. Now the film becomes a tad prosaic and literal. We get a long explanation of how, thousands of years before, teams of super heroes were created to protect the human race. (Who created them we are not told, but there's some suggestion that these super-hero teams might have been the basis of Greek mythology). Hancock and Mary are the last surviving pair, and they were engineered always to be drawn to each other. Unfortunately, as soon as they're together for any length of time, they begin to lose their powers.
The idea of a lonely and depressed super hero lost and isolated on a planet full of unremarkable humans is interesting. There's a strongly humanistic quality in the film's portrayal of Hancock. He suggests Prometheus or Milton's Satan in hell. Smith makes this part of the film interesting. But when Hancock and Mary begin wrestling with their attraction to each other and combating a criminal who wants to destroy them, the film takes on the quality of a comic book narrative and becomes less interesting. But it remains entertaining.
The coincidence that the film's second personality hinges on—that Ray Embrey happens to be married to Hancock's partner—does strain one's credulity.