Who's the guy with the book?

Obviously for the end at the park or goes through and shows all the characters as a "hey, they're still here, we didn't forget them" (except for cha cha) and just before it showed Herb and Dot, there was a guy with a book.

Who's that supposed to be? It can't be Dave since he should be dead or at least very old since he should still canonically be from the 60s. Is it supposed to be Leonard/Harrold?