One of the main reasons I was curious about this was I recently just watched the PG-13 re-release of Deadpool 2 (Once Upon A Deadpool) and at the end, there was a nice little tribute to Stan Lee where he once again talks about how surprised he is that all of his characters are so popular. Now, this makes the 3rd time (the first 2 being Deadpool and Deadpool 2) where he talks about Deadpool ads if he had some hand in creating him. Did he or was he just speaking about Marvel characters in general?
Did Stan Lee Have any input in the creation of the original comic book Deadpool?
No. Well not exactly, but there are some tenuous connections.
Rob Liefeld and Fabian Nicieza are credited as being the creators of Deadpool, but they fully admit to using a few inspirations for the character.
While many may recognise the similarities between Deadpool and the DC property Deathstroke, Liefeld has also been quoted saying that Wolverine & Spider-Man were his other inspirations.
Spider-Man, of course, was created by Stan Lee and Steve Ditko.
Wolverine was not a Stan Lee creation, but the character first appeared in an Incredible Hulk comic and the Hulk was created by Stan Lee & Jack Kirby.
Wolverine is a mutant. Mutants were brought into the Marvel continuity with the X-Men comics (yes, I know other characters have been retrofitted to be mutants), and the X-Men were another Stan Lee & Jack Kirby creation.
Deadpool first appeared in the New Mutants comic, while Stan Lee had no hand in creating the New Mutants, it was a spin-off of the X-Men.
Deadpool's character was further developed (from villain to anti-hero) as a recurring character in X-Force, again not a Stan Lee creation, but one that wouldn't have existed without X-Men.
So, to sum up. No, Stan Lee had no hand in creating Deadpool, but the character probably wouldn't exist if it wasn't for Stan Lee's many influences on the Marvel Universe.