Even though Adam Patch barely shows up to the party, he still remains a very important figure in the novel.

Related to Anthony Patch, he's Anthony's extremely wealthy grandfather who built his name on Wall Street. 

He's described as being very business-oriented and very outspoken, but also extremely judemental and not-very family-oriented (he forgot where his only son was married...)

Being Anthony's only family, Adam Patch was forced to take in his grandson after the death of his son and daughter-in-law. In all honesty, Adam Patch wasn't very happy to embark on this responsibility.

His wife had also passed away a couple years after taking Anthony in, so he really WAS the only resource.

His relationship with Anthony isn't so great either, given that he doesn't support Anthony's writing career and wished his grandson was a lot more like him - he greatly resented a lot of Anthony's dreams and desires. 

After passing away, he really proved he didn't give a slight poop about Anthony when he gave virtually nothing to his grandson in his will.

Wow.