Inception counts on a cast full of well-known actors and some frequent collaborators of Christopher Nolan, but the story is led by Dom Cobb, played by Leonardo DiCaprio, and Inception could have had a different lead as DiCaprio wasn’t Nolan's first choice. Christopher Nolan’s movies have recurrent themes, such as time and identity, and in 2010, he explored these along with dreams in Inception, which took the audience through a variety of complex layers of dreams.
Inception follows Dom Cobb, a professional thief who steals information by infiltrating the subconscious of his targets, extracting and implanting ideas in the process. When he’s offered to have his criminal history erased so he can go back to his family, Cobb takes on a complex mission that requires the help of his team, which includes architects, chemists, and more. Together, they build dream scenarios with different layers so they can extract the information they need from business heir Robert Michael Fischer (Cillian Murphy), but their mission gets more and more complicated in each layer.
Inception was the first and so far only collaboration between Leonardo DiCaprio and Christopher Nolan, and is one of his most acclaimed roles in the sci-fi genre. Although it’s now hard to imagine someone else playing Dom Cobb in Inception, DiCaprio wasn’t the first choice for the role, and it was originally offered to Brad Pitt and Will Smith, but Nolan’s way of approaching them wasn’t exactly the best, and it might have contributed to them passing on the opportunity.
According to THR, when Nolan was looking for his lead actor for Inception, he offered the script to Brad Pitt, but requested a response within 48 hours. It’s unclear if Pitt didn’t respond quickly or he simply wasn’t interested, as THR only says Pitt “didn’t commit”, so Nolan then moved on to his second choice: Will Smith. It’s also unclear why Smith didn’t take the role, but it most likely had to do with the direction his career was taking back then. When production on Inception began in mid-2009, Will Smith was on a break from acting, which started in 2008 after Seven Pounds and ended in 2012 with Men in Black 3, though he served as producer in two movies during that break (The Karate Kid and This Means War).
In Brad Pitt’s case, he wasn’t on a break from acting nor did he have a busy schedule, as in 2010 he only lent his voice to Metro Man in Megamind and he produced the movies Kick-Ass and Eat Pray Love. Of course, not starring in Inception as Dom Cobb wasn’t a tragic loss for Brad Pitt and Will Smith, as the former went on to star in projects like The Tree of Life, Moneyball, and Once Upon a Time in Hollywood, while Smith appeared in Suicide Squad, Aladdin, Bad Boys For Life, and King Richard. Having Brad Pitt or Will Smith as Dom Cobb in Inception would have surely taken the movie in a different direction, and whether it would have made it worse or better is up to the imagination of viewers.