Knife has an extremely destructive and malicious attitude, being much of a bully to victims such as Paper and Marshmallow in particular. He has shown to be lazy in "A Lemony Lesson" where he told Paper they didn't need to compete. He has the ability to cut into things due to his sharp physical nature. However, he was shown to have a soft side in spite of being so traitorous and mean, as he likes the television show Desperate Housewives and Dora Dolls. He also seems to have had a change of heart in season 2 however he is occasionally still found being a jerk.
Knife is the only contestant who knows that Microphone is working with Taco. Despite this Knife has not done anything about it. Knife also takes notice of things others don't such as seeing that Microphone keeps on going away and that Suitcase is quite depressed these days.
Official Site Bio
You could say Knife is a 'sharp guy'. He's laid back, pretty chill, but is known to be a bit lazy, and sometimes even malicious towards his fellow competitors. He can be a huge bully and sometimes seeks enjoyment out of hurting his fellow contestants. However, deep down he's a soft mushy guy who wants to just hide his insecurities and fit in.
—Inanimate Insanity Site, 2013
Knife was quickly labeled the surface level “jerk” by many, with his brash attitude and tendency to bully the other competitors. After being criticized for his criminal acts, Knife began to see the error of his ways. Knife’s heightened self-awareness has started him on a personal journey to better himself as a person. Between his newfound attentiveness and improved social game, Knife has evolved into a dangerous player.
Knife is the only character to have broken a bone during the series
In Cooking For The Grater Good, he makes a reference to the quote, "No More Mr. Knife Guy!", when Trophy gets eliminated, and soon Trophy mocks him. The reference is in fact, is a parody of a popular saying, "No More Mr. Nice Guy".
Knife is one of the characters with the least amount and the least noticeable redesigns on the whole Inanimate Insanity saga.