Liefeld created Deadpool alongside writer Fabian Nicieza in 1991's New Mutants #98, as an adversary for the young mutant team. When New Mutants relaunched as X-Force, Deadpool became a breakout character, spinning off into his own limited series, followed quickly by an ongoing series that has more or less continued in one volume or another to the present day. The character has also starred in two successful films played by Ryan Reynolds, with a third film in the works.
Plans for the Deadpool 30th anniversary celebration include a Deadpool Nerdy 30 one-shot and 30 variant covers all drawn by Liefeld, featuring Deadpool alongside other Marvel characters, including some of Liefeld's other creations and co-creations.
Additionally, starting in January, Liefeld's podcast Robservations will feature a five-part 'Making of Deadpool' series that Liefeld's announcement states will "offer insight into how the character was developed from initial discussions with Marvel to character design and beyond."
Liefeld exited Marvel in 2019 with a high-profile tweet declaring "So, this will be my last original cover for Marvel for the foreseeable future." It's unclear what if anything came of Liefeld's legal pursuit, though the tweet has since been deleted.
Oh how the time changes or the wallet needs funds!