There are two things the recently announced I Am Legend prequel won't have in common with the 2007 Will Smith-vs.-world-full-of-vampires movie I Am Legend: 1) Will Smith, and 2) A script that has anything to do with I Am Legend.
WB has decided to turn a random, unrelated script they purchased earlier this year into a prequel, one that has nothing to do with the original movie or Richard Matheson's original novel of the same name, and one that doesn't need the original movie's star. According to Deadline:
Warner is retrofitting A Garden At The End Of The World, a spec script that the studio bought back in April from Gary Graham, who was working at the Apple store in midtown Manhattan when he posted his script on the Black List website and got the attention of CAA and manager Brooklyn Weaver. They signed him and sent his script out. Amid several bids, Warner Bros acquired what was described as a sci-fi version of John Wayne's The Searchers. When Graham was brought in to rewrite his script, the studio by then had talked to the I Am Legend producers and noted enough similarities to the themes and mythology of that film that they asked the scribe to consider a redraft to fit that property.
...yeah. This always works. And the fact that the prequel won't have Smith in it and will be a prequel to a movie nearly a decade old probably won't matter, either. Yes, I sense nothing but success for this belated, half-assed attempt to cash in on blockbuster from seven years.