He's created titles spun off from his own properties, including Fray, Serenity, Buffy and Angel.
And long before he was involved with Marvel Studios, Whedon had written for Marvel Comics, on Astonishing X-Men, Runaways, and several specials, as well as making several behind-the-scenes contributions - he was a special advisor on Civil War.
He's even written for DC - albeit only once, on their Batman/Superman title.
Basically, Whedon did his homework. If Warners are serious about competing with the Avengers Assemble juggernaut, they need to find a director with a similar level of comic-book insight.
So, again, that probably rules Ben Affleck out. We know he's a comic fan, but there's a large gap between comic fan and comic creator.
It might sound like a leap, but we think that Kevin Smith might be Warners' best bet.
We know, we know, he's lost his way a little bit recently, becoming combative and contrary, particularly in his dealings with the media.
But we remember the Kevin Smith we loved, the man who made Mallrats, Clerks and Chasing Amy.
Okay, so they weren't exactly action epics, but they did contain frequent nods to comic-book lore.
Not only that, but like Whedon, Smith has written actual comics - for Marvel, and - most significantly - DC, on some of their key books.
He's even collaborated with Warner Brothers on big-screen comic-book adaptations in the past.
In fact, his involvement with the Superman franchise fell apart because he was too passionate about the source material.
In 1996 Smith pitched a Superman story to producer Jon Peters. Peters agreed to let Smith write the screenplay, with two strange conditions. One, Superman had to wear an all-black suit. Two, Superman should not fly, as it would make him look like "an overgrown boy scout."
Smith responded by handing in a script that described Superman as "a red-and-blue blur in flight, creating a sonic boom every time he flew."
That's the equivalent to Joss tearing the original Avengers Assemble script in two, and restarting from the perspective of a fan.
A large part of Avengers Assemble's appeal was the fact it looked like a live-action comic-book, complete with splash panels and two-page tracking shots. To recreate that magic, you need a director who is as comfortable writing comic-books as they are reading them.
Smith is passionate enough about Superman's comic-book identity to turn in a script the studio didn't ask for. He cares about Batman so much that, in a recent podcast, he was unable to describe an emotional scene in The Dark Knight Rises, because he was crying so hard.
He's the closest thing DC has to a Whedon, and he should be put in charge of the Justice League lead-in movies as soon as possible.
He might not have much action experience, but he can learn on the job through working with the directors of those lead-in films, gradually building to helming the Justice League movie himself.