Who is Izzy Cash from The Contract with God Trilogy: Life on Dropsie Avenue and what is their importance?

Izzy Cash, a self-made man, buys and sells clothing out of a wagon he pulls, until he can afford to buy an entire building. He is a cunning, ruthless landlord, who over time, comes around to make major donations to local charities. Izzy hires Abie Gold on retainer to manage his money after he dies.