Here's what happened to Reg Cattermole in the books:
* He worked at the Ministry of Magic in the Department of Magical Law Enforcement. This was ironic as he himself had no magic.
* He was a "rather dim" but well-meaning man. He was often teased by his wife, Mary Cattermole, for his clumsiness and lack of magical ability.
* His wife, Mary, was a witch who was heavily involved in the Ministry's anti-Muggle-born wizarding movement. This led to a lot of tension and conflict within their household.
* He was mistaken for a Death Eater by Hermione Granger during the Battle of the Department of Mysteries. This was because Mary was disguised as a Death Eater and had tried to convince Reg to join her in a scheme to get rid of Harry Potter. The whole incident led to a very awkward and embarrassing encounter with Harry, Ron, and Hermione.
* He was later found by the Order of the Phoenix and brought to safety. He was never directly involved in any more major events in the series.
In summary, Reg Cattermole remained a rather minor character throughout the series. His most significant moment was his accidental involvement in the Battle of the Department of Mysteries, which ultimately led to his and his family's safety.