The Trio is a fanon term often used to designate Harry Potter, Ron Weasley and Hermione Granger. Since the three are the central characters in all Harry Potter novels, people and events taking place in those seven years are often considered to be part of the Trio era (see the Trio-era character list).
The three friends met in their first year at Hogwarts (PS6). Ron and Harry became friends as soon as they boarded the Hogwarts Express. Hermione didn't join the group until later that year, however; she was thought of by the pair as an insufferable know-it-all. The boys couldn't stand her.
On Hallowe'en, she overheard Ron telling others of her insufferable and condescending persona, and locked herself in the girls' bathroom for the rest of the day—missing classes, even, which was a telling sign of how aggravated she was. Professor Quirrell had managed to get a mountain troll inside Hogwarts; the boys found this out and quickly concluded that the creature was heading towards that very same bathroom.
They rescued her using what little magic they knew at the time. When McGonagall, Snape and Quirrell arrived and questioned Hermione as to what had happened, she covered for Harry and Ron's rulebreaking (PS10).
From then on, the Trio became almost inseparable. Even though they often had rows for varying reasons, they usually united in times of need. Some of their most memorable arguments were:
- After encountering Fluffy, Hermione refused to speak to the boys, who didn't mind it much; they weren't friends at the time (PS9).
- Hermione reported to McGonagall that Harry had received a Firebolt as an anonymous Christmas gift (correctly guessing that Sirius Black had sent it), which made both Harry and Ron stop talking to her (PA12).
- Right after Ron and Hermione made up over the Firebolt incident, Ron went up to his room to find traces of blood on his bed, Scabbers missing, and long, ginger cat hairs on the ground. Thinking that her cat, Crookshanks, had murdered his rat, Ron once more stopped talking to her. The atmosphere between them was so dreadful that it led Harry to believe that it would be the end of their friendship for good (PA13).
- When Harry's name came out of the Goblet of Fire, Ron resented him for not sharing how to get past the Age Line; they only made up after the first task (GF17).
- After Hermione suggested that Ron had taken Felix Felicis before the Quidditch game in which he performed superby, he angrily went off and snogged Lavender Brown. Outraged, Hermione sent a flock of golden birds speeding in his direction, pecking and clawing, with the incantation Oppugno. They did not speak—or, indeed, voluntarily stay in the same room—for a long time (HBP14).
- Ron left Harry and Hermione while they were hiding in the countryside. He was angry and disappointed by Harry because they did not have a plan about how to proceed. Voldemort's Horcrux, the Locket, had a strong influence on him (DH15).
It is worth noting that, even though Harry and Hermione are very close, Ron was the one taken to the Great Lake in the second task of the Triwizard Tournament as the person Harry would most miss. Hermione was also taken hostage, but the champion whose task it was to rescue her was Viktor Krum (GF26).
The beginning of the relationship between Ron and Hermione doesn't seemed to have affected the balance of the Trio. When Harry started seeing Ginny Weasley, Ron merely gave him a jerk of head that Harry interpreted to mean something to the effect of "if you must" (GF24).