Not much is known about the early life Brock Williams, except at some point during the late 50s to early 60s, his two children Ash and Cheryl were born. He also owned a hardware store in Elk Grove, but his business closed when Ash was accused of being a serial killer.
Brock is very much like an undiluted version of his son, being far more obnoxious and racist, as he openly called Pablo an illegal and asked if he had a greencard. Later at a party he flirted aggressively with Ruby who in retaliation lifted him up by his nose. Despite his flaws, he loved his son and daughter and was heartbroken when Cheryl died and Ash abandoned him for thirty years. In his final moments, he saw his son as a hero rather than the serial killer that townfolk thought him to be.
He later returned in the third season as a freshly resurrected deadite acting revealed to be in service of Ruby. This wasn't the real Brock and Ash noticed that quickly. After Ash finished off his dad, he reappeared again, as a ghost this time.
Instead of scolding and attacking Ash like he did in the previous season, he was helpful and more friendly towards his son. He knew Ash was the hero he always wanted to become. Brock told Ash that secret that he kept to himself for a long time. The secret that he wanted to share with his son, before his untimely demise.
Years prior to Ash's return to Elk Grove, a man named Gary visited his hardware store. After a brief talk, the man turned out to be a knight of Sumeria looking for Ash. In a freak accident, Brock pushed Gary down the stairs leading to the store's basement, knocking the man unconscious. To protect his son's safety and the fear of punishment for what he did Brock barreled off the door to the basement, leaving Gary alone to die there.
In Other Media
Brock technically made his first appearance in the 2006 comic Tales of Army of Darkness in the short story Necromomicon. Him and his wife (Ash and Cheryl's mother) remained nameless for the story. In the rebooted comics, Brock and his wife (again, remaining nameless) briefly appear in a flashback that Ash has in Ash And The Army of Darkness #6.