Neville's family initially believed he might have been a Squib, but Algie was determined to catch Neville off his guard and "force some magic" from him. He once pushed Neville off the end of Blackpool pier however he nearly drowned. While over for tea one time when Neville was eight, Algie hung him out of an upstairs window by his ankles, and accidentally dropped him when he was offered a meringue by Enid. Instead of getting hurt, Neville bounced safely down the garden and out into the road, thereby proving that he was in fact a wizard. They were all so happy and Nevilles' grandmother Augusta Longbottom was crying.
Algie gave Neville his pet toad Trevor as a present for gaining entrance into Hogwarts School of Witchcraft and Wizardry in 1991. In 1995, he traveled to Assyria and brought back a Mimbulus Mimbletonia plant, which he gave to Neville for his birthday.
The Black Family Tree shows that Harfang Longbottom, and his wife Callidora, had two children a son and a daughter. While not confirmed, it is likely that the son was Neville's grandfather (and the man married to Augusta) and the daughter was, most likely, Enid, making Algie Neville's great-uncle by marriage.
Algie is a short form of the name Algernon (the original name of Augustus Rookwood), originally a Norman French name derived from aux gernons, meaning "having a moustache" This is the name of a main character in Oscar Wilde's The Importance of Being Earnest. Algie is also a homophone of the plant-like organisms algae, possibly referring to the interest in Herbology that Algie and his great-nephew seem to share.
- Harry Potter and the Philosopher's Stone (First mentioned)
- Harry Potter and the Order of the Phoenix (Mentioned only)