Carson the
muskrat is a character created by
John Kovalic, originally for his
comic strip Wild Life and later used in his
other strip,
Dork Tower.
In Wild Life, Carson served as a sort of Charlie Brown figure - the most main character of an ensemble. In Dork Tower, he is more of a side character, but still with the everyman characteristics - in a strip about the geeks, dorks, and other outsiders of society, Carson is the one closest to center. Except for the muskrat bit.
He looks more like a brown sheep with a big black nose than a muskrat.