I Am Legend's entire concept is built around the notion of the supposed last human alive, but an early, terrible idea would have cut the apocalypse completely. I Am Legend is based on a 1954 novel by Richard Matheson, who was inspired to write the book based on the notion that if Dracula was so scary, then a world filled with vampires must be horrifying. He was correct, with the post-apocalyptic horror novel being influential on the likes of Stephen King and George A Romero, who based Night Of The Living Dead on the book's siege scenario.
I Am Legend - which has a superior alternate ending - received two movie adaptations in the years that followed; the first was 1964's The Last Man On Earth starring Vincent Price, while 1971's The Omega Man was fronted by Charlton Heston. The latter had little in common with the novel and while Matheson contributed to The Last Man On Earth's screenplay, he was disappointed with the low-budget final product. The Will Smith version of I Am Legend spent around a decade in development, and at one stage almost starred Arnold Schwarzenegger with Ridley Scott directing.
Screenwriter Mark Protosevich wrote an acclaimed script for I Am Legend during the '90s, which was considered - for a time - to be one of the greatest underproduced screenplays of all time. Will Smith's eventual I Am Legend (which has a very different ending to the book) did lift some sequences and ideas from this draft, including expanding on the relationship between Smith's Neville and his dog, but it changed a lot too. Protosevich later spoke about I Am Legend's long development with Money Into Light in 2013, and revealed the movie's co-writer and co-producer Akiva Goldsman wanted to change the core idea. Instead of the world being infected, he wanted to limit the outbreak to New York, with Neville being the only human to remain on the quarantined island while the rest of the planet was fine.
Given that the basic premise behind I Am Legend focuses on what might be the last remaining person in a world filled with vampires/Darkseekers, this change sounds like a terrible idea. According to Protosevich, in Goldman's take "Neville chooses to remain on the island to do his research because his infected wife and child are there. The inherent threat was that if the 'zombies' escaped the island, the outbreak would spread." While Protosevich was offered the chance to pen this version of I Am Legend, he felt it had major problems but when he presented those issues to Goldsman, he was let go from the project.
When I Am Legend was finally announced, Protosevich was surprised to learn this concept had been abandoned, with Warner Bros rejecting Goldsman's softened take. Not only did the resulting I Am Legend film restore the "Last Man on Earth" premise, but the film also received praise for managing to smuggle a character drama into a blockbuster package. The movie also proved to be a major success, though it's hard to say if audiences would have been so drawn to the idea had the apocalypse concept been dropped.