He is Andy and Jen Larkin's Father and Freida's husband. He works at the local toilet paper factory and was once the mysterious prankster of East Gackle when he was a teenager.
Al is usually annoyed with his son's compulsive pranking and has threatened to send him to military school and his cousin Alward's farm to straighten him out, he had also lost his job a few times from his son's stunts, but Andy has always made up for his mistakes and uses his pranking abilities to help his dad get his job back and get him out of trouble. Regardless, Al is actually proud of his son and finds most of his pranks hilarious.
When Al was young, he was a prankster like his son and his father but kept his identity as the mystery prankster from his family. Al probably kept it a secret from his son, daughter, wife and possibly his father because when he was growing up he saw his father (Andy's grandfather) receive a lot of ridicule and backlash for his own pranks and humiliated his son a few times from them, like on Al and Freida's wedding when his father dressed up as a gorilla and caused chaos, while Al had a passion for pranking like Andy did in his youth he possibly feared the consequences if he were to get caught and did his pranks in secret so East Gackle wouldn't know it was him so he wouldn't be shunned.
It is also possible he was dating Freida when they were in school since the mystery prankster pulled pranks when they were young. Soon Al met Miss. Murphy, the school councilor, it is possible she found out Al was the mystery prankster when she found his plans for what would of been his last prank: The Lamb chop Caper, it can be speculated that she gave him the ultimatum that he either let her stop his pranking forever with her treatment or she would tell everyone who the mystery prankster is and he would be in trouble, and Al had no choice but to let her do it, after he received the hypnosis Miss.Murphy promised to keep the mystery prankster's identity confidential for his sake since he will no longer be pranking. It is assumed that her hypno therapy failed since Al marveled at the lamb chop caper prank his son pulled, the prank he never got a chance to pull and at the rodeo he helped Andy and Danny get Lick, Leech and Mr. Leech disqualified by having Andy spray Cow must on them and have the bull chase after them, so it is possible that Al is still a prankster but keeps himself under control so he won't embarrass his family but often times helps his son with some of his pranks, even though his son has no idea his father was once a famous prankster.