The most notable thing about Mr. Pignati in The Pigman, by Paul Zindel, is the fact that he is a widower. His life is now shaped by the death of his wife and the grief he feels at this loss.
He is a retired electrician who lives alone in John and Lorraine's neighborhood. He is not a small man and his house is quite unkempt. When the two kids meet Mr. Pignati, he does not (cannot?) tell them that his wife, Conchetta, is dead; he says she is on an extended trip. He is a very lonely man, as evidenced by the fact that he visits the zoo nearly every day and calls Bobo the gorilla his best friend.
No one but Mr. Pignati has anything nice to say about Bobo. Lorraine says he is the "ugliest, most vicious-looking baboon," and one of the zoo attendants feels "that baboon had the nastiest disposition around here." Despite these characterizations, Mr. Pignati talks to Bobo as if he were a baby.
Mr. Pignati has a pig collection which he adores but which John, at least, finds bizarre.
There were pigs all over the place. It was ridiculous. I never saw so many pigs. I don't mean the live kind; these were phony pigs. There were glass pigs and clay pigs and marble pigs.
Because Mr. Pignati is desperately lonely, he befriends the two kids and wants to take them to places he loves (like the zoo) and share with them things that are meaningful to him (his pig collection). This friendship seems to be the only human contact he has, and he finds his relationship with John and Lorraine quite meaningful. Mr. Pignati is a bit of a tragic figure, spared from complete tragedy by the few highlights in his life.