Backstory
Much of Lurch's history, including his first name and the nature of his relationship to any other Addamses, was originally unspecified. "Lurch" was revealed during the original TV series to be a surname, as there was a "Mother Lurch" who appeared in one episode. She addressed Lurch as "Sonny", which could either be a parental nickname or his actual first name. As for his father, he was mentioned once in the second animated series, and in an apparent reference to his Frankenstein's monster-like appearance, Lurch said, smiling, "He put me together."
It was stated in Addams Family Reunion that Lurch is part Addams. This plays into his being a creation similar to Frankenstein's monster. The only definite body part that is from an Addams is his heart. Lurch's mother appears to be a physically normal, elderly woman, although she does not see anything unusual about the Addams family or their home, with the exception of Thing.
In The New Addams Family, a woman comments to Morticia about Lurch, "Where did you dig him up?", to which Morticia responds, "Funny, I can't remember which cemetery it was." Lurch is also referenced as having "two left feet."
Read more about this topic: Lurch (The Addams Family)