The reason he is a miser is because he had to scrounge for food and save everything in the Holocaust.
Vladek, in one instance, is walking along the road with Artie when he finds telephone wire. He says that telephone wire is very useful because it has little strands inside that are good for tieing things together. When Artie says that to just buy it at the store, Vladek scoffs, telling Artie that buying costs money and this was free. This is a clear sign of someone having to have lived at some point through rough times, in which they needed to search for even the simplest of things. The second way Vladek changes is he becomes much more depressed throughout the Holocaust.
He sees many people die, some of which he knew very well. Penultimately, gives his little boy, Richieu, to Tosha, who was also hiding two other kids in her house. Tosha lives in Zowiercie. One day, the Nazis decide to clear out the rest of that ghetto. When Tosha finds out, she poisons herself and all three kids, including Richieu. Vladek found out much later that his child was poisoned by the very person he trusted to keep Richieu safe. Finally, when he arrives back from the Holocaust, his wife, Anja, commits suicide, leaving Vladek destitute. Artie stays with Vladek on the night of Anja's suicide and comforts him, while Vladek mumbles and moans the whole night through. That night, they sleep on the floor. At the funeral, Vladek jumps onto the casket and cries for Anja. It was very obvious