Kat is the leader of the pack in almost every way. He supported his friends who have realized that the teachings of Kantorek are simply empty cliches.
Stanislaus Katczinsky (Kat) has a distinctive sixth sense in identifying trouble and food, which the other men admire greatly.
He also seems to have some sympathy with Communism, although this is not well developed in the novel.
He believes in duty. And despite not personally embracing the ideals that drew him to this war, he fights his heart out. Kat's big moments in the book come from resolving little conflicts, from finding and killing the wild goose, to, in the end, dying from a shrapnel wound in the head after a bullet has hit his shin.
Here's a plot overview from Sparknotes.com.