By that token, Frazz has been described as a grown up Calvin
Swedish comic Rocky featured a strip in which the title character's comic is rejected because the publisher claims that its protaganist is an Expy of Fritz the Cat. Another strip suggested that the title character in a similar comic, Elvis, was an Expy of Rocky.
Now-extinct British newspaper strip The Perishers features expies of multiple Peanuts characters - Old Boot is very similar to Snoopy, and Maisie is virtually a clone of Lucy van Pelt, with her younger brother Baby Grumpling having several of Linus's traits.
