Sure he is -- not in a legal sense, but certainly in a cultural sense.

To pick another comic from the era, the Far Side doesn't have a central character or set of characters like Calvin & Hobbes. There may be a recurring cast of similar bovine, but they aren't characters in the same way Calvin and Hobbes are. Is C&H more worthy of copyright protection? Copying any one comic would be violation of copyright, but if I make another comic with talking cows, no one will say that I sole from the Far Side... well they may say it, but it would be hard to prove.

Once published, these original works become part of our culture. If someone draws a young boy with a stuffed tiger and makes no claim that the characters are to depict Calvin and Hobbes, how can someone claim that they are protected from copyright anymore so than taking cows?

If I have the choice of buying a t-shirt that Bill Watterson illustrated, or some knock-off imitation that claims to be illustrated by Bill Watterson, Bill should be able to sue to protect his name. But if the illustration makes no claim to have been authored by Bill Watterson, why shouldn't this be allowed? Side by side on a clothing rack, I'd buy the official C&H design over an imitation, provided that the official design was the funnier shirt. If the "imitation" design is funnier, then do we as a culture not benefit from what would today be categorized as copyright infringement?

With Full Screen Mario, no claim is made that this is created by Nintendo. If you recolored the art, so that Mario had purple overalls and a yellow shirt, is that sufficiently different? At what point has something been altered enough so that the derivative work isn't a "copy?" Can Nintendo lay claim to the color palette chosen?

The reality is that the line drawn between what is the original and what is copyright infringement is indefinable. More to the point, it is a legal question answered by a court, and therefore an objective decision. Characters are just as much a part of the culture as are the style and format. It just so happens that our current laws favor the protection of characters. If your character is overwhelmingly recognizable in "derivative" works, copyright holders can claim infringement, even when copying wasn't a part of the creative process. Even if the "derivative" work is substantially different in terms of how the asset is used.

As a culture, we really need to reflect upon why we have copyright protection in the first place. I'm convinced that it is causing more harm than good. Copyright is meant to expire so that the culture can build upon concepts and ideas that are still relatable to the culture in which the original was established. 25 years is more than ample time for the original copyright owner to have benefited from an idea. There is no harm to our culture if those ideas are allowed to flourish under the stewardship of others. With the accelerated pace or society evolves today, 25 years is downright ancient.

Full Screen Mario is obviously intended to look and feel like the original game Nintendo published 30 years ago, but so much has changed since then. If Nintendo created Super Mario Brothers today, and they were just getting into the gaming industry, I don't think they would have even built the game using web technologies... they probably would have created a game that runs on cellphones and tablets and they would have called the game Angry Birds.

Rovio understands current copyright law as much as anyone, which is why their games have recognizable characters. Sling shots can be replaced with catapults and birds could be replaced with squirrels, and no one would mistake that game for Angry Birds, even with similar game play mechanics. If you were to put a red bird with a yellow beak in a racing game, I would be terribly surprised if the creators of the driving game weren't sued. Has our culture been harmed in either instance? Has Rovio been damaged in one instance more than the other? Does our culture benefit from any of this copyright debate?