Who is Old Man Regan from Pictures of Hollis Woods and what is their importance?

Old Man Regan is the father of the Regan family. He is an architect. Hollis loves the Old Man, but she blames herself for his arguments with Steven. When the Old Man blames Steven for the truck accident on the mountain, Hollis runs away before she can ruin the entire family. The Old Man visits her at the agency and tries to convince her to come home, but she refuses. When Hollis runs away with Josie, the Old Man searches for her, traveling between Hancock and Long Island frequently.