Um… Not since the beginning – he’s not really defined in New Mutants #98.
In fact, it would have been a lot better if Bob Harras and Marvel did not let happen what it happened but… oh, well.
But they gave him character afterwards, that is undeniable, otherwise no one would be looking for NM#98 or early X-Force…
True. Wasn't until the late 90's Deadpool was defined (and continued to evolve). Regardless, he was a head of his time, and it took hime a very long time to find broad acceptance. Some people still have difficulty accepting him as a real character.