Although Deadpool holds the title of being Marvel's most contemporary fourth-wall-breaking character, he's far from the first. Before the merc with a mouth became the comedic flagship at Marvel, She-Hulk preceded him in the 80s with John Byrne's legendary run that's filled to the brim with metatextual comedy. And prior to She-Hulk's time in the limelight, Howard the Duck was Marvel's resident gag character and arguably their most successful.
While most might remember him from the 80s Hollywood bomb Howard the Duck, studious comic fans remember Howard as a fixture of Marvel's 70s scene. Despite getting into several conflicts in the confines of his book, some of Howard's most notable fights happened outside of the comics. For example, as the fowl soared to dizzying heights of popularity, Disney, who now owns Marvel, tried to clip Howard's wings by alleging that he was too similar to Donald Duck in a brief legal dust-up. However, the Disney suit wasn't the only legal battle that Howard faced during his lifespan. At one point, Marvel and Howard's creator Steve Gerber found themselves in a legal dogfight over the character. In the video linked above, the YouTube channel Comic Tropes goes over the battle and its ramifications in full.