Harold Kaczmarek is Clay Kaczmarek's father, who came from a family of engineers.
In Clay's youth, the boy aspired to be something greater, such as an astronaut, though his father preferred to steer him towards the family occupation. As such, Harold often called on Clay to help him with his building work.
When given the news that Clay had gotten into an institution for engineering, Harold was disappointed to learn that Clay had not been accepted into one of the top academies and that he was to become a computer engineer.
Owning a construction firm, Harold's business faltered sometime around the early 2010s, prompting his wife to leave him and Clay, and forcing him to rely on his son for payments in the forms of checks to keep himself afloat in the economic downturn.
On the 27th of January 2011, four days before Clay was captured by Abstergo's Lineage Research and Acquisition, Harold tried to contact Clay over the phone. He left a message stating that he and Clay had not spoken in a long time and that he wanted Clay to come home and help him fix the back porch of the house. In the end, Harold concluded the message by asking Clay to just let him know if he was okay.