Five years ago the makers of South Park planned to air an image of the Prophet Mohamed during an episode, but their network Comedy Central eventually decided to self-censor.
In Sunni Islam, visual depictions of Mohamed are considered prohibited, and South Park creators Trey Parker and Matt Stone received death threats in the build-up to the much-hyped episode.
In response to those threats, Seattle-based cartoonist Molly Norris created 'Everybody Draw Mohamed Day' on May 20 of that year, with people encouraged to draw their own versions of the Prophet and share them online.
Three suspected Islamist extremists burst into Charlie Hebdo's Paris office yesterday, killing 12 people in total.
At least two suspects remain at large and no official motive has yet been established, but the attack is believed to be linked to the magazine publishing cartoons of Mohamed in the past, an incident which saw their offices firebombed in 2011.