Book 1 vs. Season 1: Catelyn on the Sidelines
Catelyn Stark is a character adapted patchily in season one, and sad to say, that’s about the best of the adaptation she sees. The show did an excellent job (for the most part) in capturing her concern for her family and how love for them motivates most everything she does, good and bad, wise and unwise.
But for Catelyn, being a wife and mother encompasses more than just keeping house and watching over her children. Her dynastic ambitions far outstrip those of her husband, she’s a capable diplomat and high-level political advisor, and pretty much any book scene where she watches military planning demonstrates she has a working knowledge of strategy (though very little confidence in that knowledge). She sees using those skills as part of her duty to House Stark. This aspect of her personality is lost mostly in the front end of season one, when the show wishes to make those vital first impressions.
In the back end of season one, a new issue emerges. Though book!Catelyn and show!Catelyn are never again closer to being the same character, show!Catelyn must compete with Robb for the focus of the storyline, and it’s a competition Catelyn loses comprehensively.