Cosmo Kramer (Michael Richards)

Kramer has many conflicting personality traits. Described in "The Letter" by an art patron as "a loathsome, offensive brute", he is often shallow, callous, and indifferent. On the other hand, he is often caring and friendly, going out of his way to get his friends to help others and to do the right thing even when they don't want him to.

Kramer is known for his extreme honesty and, correspondingly, his lack of tact; in "The Nose Job", he tells George's girlfriend that she "needs a nose job". Instead of being horrified, many characters end up thanking Kramer for his candor. Kramer never gets into trouble for it, but his friends often do. He also gets his friends into trouble by talking them into things such as parking illegally in a handicapped space ("The Handicap Spot") or urinating in a parking garage ("The Parking Garage").

Kramer is known for appropriating items from Jerry, most notably food. Jerry's apartment is Kramer's second home (at one point he calls Jerry's phone line one, and his own line two); he has his own key to the apartment, almost never bothers to knock, and even begins to receive phone calls there in "The Pilot, Part 1". It is revealed in "The Betrayal" that this may be due to Jerry's offer upon moving into the building (12 years earlier, about 4 years before the first episode), telling Kramer "We're neighbors. What's mine is yours."

Much of Kramer's lifestyle is "out of date", including his clothing, which is often a size too small and years (or decades) out of fashion. He seems to shop at second-hand stores and has no concept of style or taste. Kramer thinks of himself as a very "with-it" individual, up-to-date on everything, but is constantly being shown to be ignorant, uninformed, and foolish. He often drives large, old American sedans, such as a 1973 Chevrolet Impala, or a 1985 Ford LTD. To all this, Kramer is oblivious and he takes no note of other people's opinions of his lifestyle and views.

Kramer's own apartment is sub-let from documentary filmmaker Paul Buchman from Mad About You. Kramer's apartment is the subject of numerous radical experiments in interior design, including "levels" (no furniture) in "The Pony Remark", and a reconstruction of the set of The Merv Griffin Show in "The Merv Griffin Show".

Kramer's signature on the show is entering a room sliding in, much like Art Carney's character in The Honeymooners. This reportedly first became a recurring gag when Richards was late for a cue; trying to save the scene, he burst into the room, much to the delight of the audience. His initial bursts into Jerry's apartment were fairly conventional, and became somewhat more flamboyant or physically comedic as the series progressed. He is also known to be very clumsy, constantly tripping over things and knocking things down.

George Costanza once commented, upon hearing that Kramer had gone to a baseball fantasy camp, that Kramer's whole life was a fantasy camp: "People should plunk down two thousand dollars to live like him for a week: Do nothing, fall ass-backwards into money, mooch food off your neighbors, and have sex without dating! That's a fantasy camp!" ("The Visa").

Cosmo was known only as "Kramer" during the show's first five seasons (from 1990 to 1994), In the first (pilot) episode, however, his name was actually Kessler. It was George who found out his unusual first name through an encounter with Kramer's long estranged mother, Babs (played by Sheree North), on the season six episode, "The Switch". Despite this, most characters continued to call him Kramer for the remainder of the show's run although many minor characters did begin referring to him as "Cosmo".

Like the other three characters, Kramer has pseudonyms he uses in various schemes; H. E. (or A.G.) Pennypacker, Dr. Van Nostrand, and Peter Van Nostrum are the most popular. Nostrum means "unverified science of dubious origin" or "a questionable scheme".