When we first meet the K-Man, he is a boorish and bohemian character....a scammer with low energy levels. Relying on his rent-controlled apartment and residual income from his Calvin Kline underwear ads etc, he has a freedom that is both envied and misunderstood by his friends. Kramer evolves over time into an energetic and eccentric character who has risen above his upbringing. He yearns to be a father and push his genes out but he knows this will never happen. He moves effortlessly from protege to mentor, the former particularly if it involves golf. Kramer's dysfunctional family and childhood (witness his mother and his fear of clowns) has left some scars on him but it's this that allows him to empathize with other eccentrics eg the Soup Nazi.
There is a generation gap between Kramer and his friends - he's the 'outsider'. Kramer has 'causes' (mostly to do with retailers) eg his strike stance at the pizza shop, the fruit vendor, the coffee conglomerate and Kenny's chicken ("it's the wood that makes it good" LOL!) but he won't let his causes stand in the way of his appetite or self-interest, whether it be his love of hickory chicken or protecting an Armoir.
Kramer is the least hung-up of the main characters.....could you imagine George, Jerry or Elaine openly discussing a lack of peristalsis?
He is probably the most complex character too (maybe it has to do with 'levels' ;>), and it's very difficult to accurately sum him up succinctly. Perhaps Elaine put it best....he's a 'hipster dufus' and we love him for it. If you don't like Kramer, you might agree with...."He is a loathsome, offensive brute...yet I can't look away".
Peter