Author's Note(s): I wrote this for the Harry Potter Random Fact Fest. I hope that some of the specific info is correct, if not, I tried. I hope you enjoy!
1. Hagrid was taking a visit in Hogsmeade one spring day of his first year at Hogwarts. He noticed a shady looking figure lurking in the distance, and was very nervous when this figure approached him. He didn't introduce himself, but instead presented Hagrid with a shiny gold box, about the size of a baseball, and told him he would trade him this mysterious box for the candy he'd just bought at Honeydukes. Being a curious kid, Hagrid accepted the offer, not knowing what was inside.
2. Although it couldn't yet see, the creature that was inside knew that things were changing. He'd spent many weeks in that warm box, listening to his previous owner yell at his mother. He knew that this was for the better He wasn't scared, but he was a bit apprehensive as to what to expect, seeing as he hadn't even hatched yet.
3. Once Hagrid got back to Hogwarts, he immediately raced up the stairs to his bed, tearing open the box. He was very excited about the contents of the box. An egg, about the size of a golf ball, sat in the middle of what looked to Hagrid like a web-like substance. Hagrid's favourite subject in school was Care of Magical Creatures, so receiving an animal of his very own was a dream come true. Hearing Hagrid's friendly voice, Aragog knew at once that his new owner would care for him much better than his previous owner, and was eager to hatch and finally meet him.
4. Over the next few days, Hagrid made sure that his new egg was comfortable. He wasn't sure what to expect when it finally did hatch, maybe a bird? Or a dragon? He knew he had to keep it warm, and every once in a while he'd take it out of the protective box and hold it in his hands, rocking it back and forth. Aragog loved the effort that was being put forth toward him, but he didn't like the roller coaster feeling of being swung about.
5. Aragog finally hatched on April 13, 1942, only 4 days after Hagrid brought him to Hogwarts. Hagrid was surprised when the egg hatched, and out crawled a little spider. There was never any fear of him, as Hagrid accepted all kinds of creatures, and as soon as Aragog set his many eyes on Hagrid, he knew it was a match made in heaven.
6. Hagrid hadn't come up with a name for Aragog until weeks later, referring to him as "Little Buddy" until the perfect name came to him. Hagrid, having to hide him in the Room of Requirement, so that other students wouldn't find him, made sure to bring food to him every day. It soon became apparent that Little Buddy wasn't just any spider, he was growing at a rapid pace, eventually not able to fit in the little cupboard that sat in the middle of the room, and Hagrid decided to name him Aragog, meaning Giant Spider in Latin. Aragog was pleased with his name, but loved it even more when Hagrid still called him his pet name.
7. One of the only two times that Aragog was ever afraid was when Hagrid got expelled after Tom Riddle found out about him. He was afraid that his owner, his friend, would forget about him, and he'd never see him again. The night that Hagrid was to leave the castle, he came and got Aragog, taking him out of the castle with him, leaving him in the forest. Aragog had no idea what to expect in the wild, but he knew it wasn't Hagrid's fault.
8. In the years to follow Hagrid's expulsion, Aragog started to lose hope that Hagrid still cared about him. He knew he still lived on the grounds, and fell into a deep depression due to loneliness. All he had in the forest were the squirrels that would unknowingly stumble upon him, but since Hagrid never brought him food, he was forced to eat them.
9. After 5 years of never seeing him, Hagrid finally showed up to Aragog's territory. Feeling a little bitter at first, Aragog tried to ignore Hagrid, but after 10 minutes of Hagrid begging and sobbing, Aragog finally broke down and spoke to him. After Hagrid explained that he was helping Dumbledore out with the castle grounds, and that he really couldn't get away until now, Aragog forgave him, and Hagrid promised to come check up on him at least once a week. Aragog thanked him, and told him how lonely he'd been, and Hagrid said he'd have a surprise for him the next time they saw each other.
10. In the week before Hagrid's return, Aragog felt nervous about what Hagrid's surprise could be. When the day finally came, Hagrid was carrying a large box, the size of a washing machine. Aragog was confused, but when Hagrid revealed what was inside, he was both relieved and appreciative. Hagrid had found a friend for Aragog, who's name was Mosag. She was slightly smaller than Aragog was, but upon seeing her, he knew it was love at first sight.
11. When Hagrid finally left the two alone, they started talking. Aragog asked her where she came from, seeing as he had no idea where he'd come from, all Hagrid knew was that a strange man had given him to him in town. It turned out that Mosag had come from a place called Middle Earth, a place with hobbits, and orcs, and her master had been a horrible spider named Shelob. Her job was to terrorize anyone who came near their territory, but she felt that she couldn't fulfill her duty, and managed to escape one night while Shelob was asleep. Aragog thought this was all strange, but after a few minutes he accepted it, remembering that where he lived, wizards, and goblins, and other strange creatures, ran rampant.
12. After only 6 months of meeting Mosag, Aragog knew that he wanted to spend the rest of his life with her, romantically. He wasn't sure if two acromantulas getting married was normal, but he wanted it. Since there really wasn't anyone who could legally marry them, they asked Hagrid to do the honors, and on November 3, 1950, Aragog and Mosag held a small ceremony, in which a few of the centaurs in the forest, and Dumbledore, in secret, were invited and watched. Aragog never told Hagrid that Dumbledore knew about him, and often checked up on him.
13. Aragog first met Dumbledore while the wizard was walking through the forest, eating colourful beans, all the while complaining that they tasted like vomit. Aragog thought the man was crazy, but after one visit from him, he found him to be delightful company, but Dumbledore, for some unknown reason, told Aragog to keep it a secret from Hagrid that they met occasionally. Aragog later realised that this was because Hagrid didn't have any other friends, and Dumbledore didn't want him to think he was taking him away from him.
14. The second time Aragog was afraid was the day that Mosag told him she was pregnant. Aragog sat around for an entire week, worrying about whether he'd be a decent father or not. When the day finally arrived, Mosag's 1000+ eggs hatched, and the little spiders immediately took to Aragog, wiping away all his fear. Hagrid often visited, bring with him scraps of food for the little tykes. Hagrid even helped to name some of the children, but he secretly forgot most of them, understandably. Aragog knew he couldn't tell them apart, but never said anything.
15. One day while hunting for food in the forest, Aragog came across a Hogwarts student who looked like he was in immense pain. He learned that the student's name was Remus Lupin, and he was recovering after the full moon forced him to turn from human, to werewolf, to human again. Remus had nowhere else to go, for fear of hurting his fellow students, so he would go out to the forest once a month and let his curse run its course. Aragog urged him to visit him when he was in human form, and they became good friends, not as good as Aragog and Hagrid were, but good friends none the less. Remus stopped coming to the forest as often as he had before once Dumbledore provided him with the Shrieking Shack, but he still came when he wasn't a werewolf.
16. One of Aragog's favourite past times were going to the lake on the Hogwarts ground after dark, and taking a swim with Hagrid, who used the lake to bathe. They would swim for hours sometimes, until Mosag would come looking for him, alerting him that she was going to sleep. Aragog also enjoyed what he and Mosag would call tight rope walking. He would make sure there were eight thin webs running from one tree to another, and walk the length of them. Sometimes he would fall, and Hagrid would come rushing into the forest, as the tremble of the fall would startle him. He was never hurt.
17. When Remus Lupin was added onto the staff of Hogwarts many many years later, he was sure to visit Aragog occasionally. When Remus told Aragog about Ronald Weasley's fear of spiders, and about how hisboggart had been a spider, and he'd put roller skates on it, Aragog had a good laugh at it. The two thought it would be funny to get four pairs of roller skates and put them on Aragog, so they did, Remus taking a picture of it. Remus kept that picture in his top drawer, along with other sentimental pictures he kept of his friends.
18. The day that Dumbledore died, Aragog was greatly depressed. Mosag tried everything in her power to get Aragog to act normally, but there was nothing she could do. She'd met Dumbledore, but didn't know him as well as Aragog had. On the day of the funeral, Aragog came out of hiding and attended the ceremony. It was one of the worst days of his life.
19. After Dumbledore's death, Aragog was a lot less active than he'd been his entire life. He started to get sicker and sicker, and Hagrid did all he could to bring him back to great health. He'd learned that his favourite thing to eat was chicken soup, and could understand why humans would prefer to eat it when the became ill. It did nothing to make him feel any better, but he knew it made Hagrid happy to know he was doing his part to help.
20. Aragog died at an old age, of natural causes, something that Hagrid didn't understand, no matter how much Mosag, or anyone else, told him. Hagrid thought that there must have been something else he could do to save him, but it wasn't true. Aragog lived a long, wonderful life, and had a wonderful caring family. Mosag was devastated when Aragog had died, and was so proud when Hagrid hadburied him. From then on, Hagrid felt like a little part of him was missing. He often visited Mosag and the children afterward.