Calvin is named after John Calvin (1509-1564), a leader of the Reformation. John Calvin was well-known for expressing his opinions in a most lucid, logical and convincing manner. Six-year old Calvin is similarly eloquent in the expression of his opinions and attitudes, though his opinions differ greatly.
Although Calvin is a six-year old, his contemplations and observations of the world around him are often extremely insightful. Calvin's curiosity and imagination often get him into trouble. He's not really a brat, just an interesting mixture of immaturity and innate wisdom.
Hobbes is named after Thomas Hobbes (1588-1679), a philosopher who had a low opinion of human nature. Hobbes, Calvin's tiger friend, is a bit more upbeat but seems to possess an opinion of humans similar to his namesake. It seems that one of the only things Hobbes does which bother Calvin (beside frequent pouncings) is the enjoyment he derives from gloating about being a tiger.
Calvin's Dad is nameless, but is apparently a satirical portrayal of Bill Watterson's own father. (In fact, Calvin's dad is a patent attorney, like Watterson's father). Watterson explains that most of Calvin's camping trips which involve "character building" are relatively unaltered versions of the trips his own dad used to take him on, while Watterson was a kid. Calvin's Dad is extremely amusing, from his explanation of natural events (which often become more complicated than the real explanation) to his reaction to Calvin's "escapades". He is fairly level-headed, sometimes sarcastic: often with a strange twist of humor. He probably enjoys Calvin a lot, though he did claim that what he really wanted was a dog!
Calvin's Mom is nameless as well. She's hardworking and is always there when Calvin is in real trouble, like when Calvin accidentally rolls the car into a ditch, or when Hobbes is really lost, or when Calvin is sick. She's about as perfect a mom as you could expect- especially with a son like Calvin. Of course, Calvin's Mom is exasperated by Calvin at times, too. Parenting Calvin is a tough job, its amazing that she's still sane. Watterson's own comments on Calvin's mom: "The daily disciplinarian, a job which taxes her sanity... so I don't think we get to see her at her best. I regret that the strip mostly shows her impatient side, but I try to hint at other aspects of her personality and her interests by what she's doing when Calvin barges in."
Susie Derkins is the perfect, "A" student kid who lives next door. She is a girl who Watterson describes as "earnest, serious and smart". She serves as an excellent foil for Calvin's personality - and Hobbes', as well. Susie and Calvin have a love-hate relationship which is based on mostly intense dislike. Calvin rarely does anything worse than kidnapping Mr. Bun or pelting Susie with snowballs while contemplating the effect of his actions on Christmas morning. Susie is by no means a sitting duck either, as she's often the one who has the last laugh in most of Calvin's schemes.