Deadpool showed up in the final moments of the first stand-alone Wolverine movie, complete with a mouth that was sewn shut. It was an odd design choice for a character who is literally called "the merc with the mouth."
Deadpool is known for understanding the fact that he's in a comic book, he's hyper-violent and seems to be invulnerable. In some ways, he's the Joker mixed with the Wolverine.
The character is, to put it bluntly, frickin' awesome.
Some leaked footage from what was meant to be a standalone Deadpool film has been released online, and it features everything fans love about the character. It's funny, people die and Ryan Reynolds does a pretty great job with the voice. It's a teaser that begins with Deadpool singing Gwen Stefani and ends with him playing with a decapitated head, so I'd also label it not safe for work.
Deadpool's creator, Robert Liefeld, discussed the footage briefly on his Twitter account.
To ALL who have enjoyed seeing the DP footage, enjoy it for what it is. Test's are done for films all the time and you have glimpsed process— robertliefeld (@robertliefeld) July 29, 2014
The footage is likely a few years old, which explains the "Hi Tom" quote that ends the teaser. Tom Rothman was the CEO of Fox until September 2012, and that moment was likely meant to tickle his funny bone. It also shows that everyone involved clearly understands Deadpool; this was the character asking for a greenlight for a full film.
One day, perhaps.