So, what is an animagus? Or in plural, what are animagi?

An animagus is someone who can transform from human to animal form, and of course back to human. The word is a mix between the words "animal" and "magus", which means magician in Latin. So animagus means animal wizard.

Some famous animagi include The Maradeurs; Sirius Black who was a dog (Padfoot), James Potter, a stag (Prongs), and Peter Pettigrew, a rat (Wormtail). Part of the group was also Remus Lupin, but he was no animagus, he was a werewolf, and the reason that his friends transformed. Minerva McGonagall was also an animagus, she was a cat. One not-quite-as-famous animagus was Rita Skeeter, yes, the journalist. Her form was a beetle, which is quite convenient if you're a journalist. 

However, the fact her form was so convenient was no surprise - your animagus is not coincidental. It's based off your personality, you. It's the animal that suits you best. It's normal for a persons animagus is the same as their patronous.

If there is anyone who reads this book to become an animagus, I suggest you read the whole book before you try. The process of becoming one is very complex, long and if done even slightly wrong might have horrible consequences. What you should also know is that there exists a register of animagi that the Ministry of Magic holds, and every animagus that exists should be registered to be legal. If you're an unregistered animagus, it has it's perks of course, going unseen, but then you'd be an animagus illegaly, so beware.

Some famous unregistered animagi that we know of include Sirius Black, James Potter, Peter Pettigrew and Rita Skeeter. Being unregistered is a big perk, as long as you don't get caught. For example Mr. Pettigrew, who later served under Voldemort, could be running around unseen and unknown of, 'cause he was not registered. He lived as a rat for 12 years, everyone believing he was dead or disappeared, while he was right under their noses. Same with Rita Skeeter, being an unregistered, a.k.a. unkown of animagus beetle, is VERY convenient for a journalist to eavesdrop and write the most interesting stories. Minerva McGonagall was registered.

There is, of course more reasons for people of the past to have been unregistered. There lived an animagus, an eagle,  who was unregistered. Out of fear. His mother had been a registered animagus, a white swan. But since his family fought against Voldemort at the time, they could easily find the mother and cross her off, and they did. So Talbott Winger, the boy, his fear was justified. Professor McGonagall was one peson who knew about him being an animagus, and she respected his decision to stay secret.

However it's no surprise that, if you get caught being an unregistered animagus there is consequences. It's illegal after all. If you're found out and the Ministry of Magic get you, you'll be sent to Azkaban. The amount of time you'll have to spend there is unknown, but going to Azkaban is, even for a short amount of time, not pleasent. So I suggest you get registered, but if you decide to stay unregistsered then atleast avoid getting found out. 

Animagus have been around for long, as long as wizards. Morgan le Fay was a bird animagus, and Lisette de Lapin was suspected to be a white rabbit.

The first ever animagus that was known, was an ancient Greek wizard, Falco Aesalon who could turn into a falcon.

Ps. Sorry if there's any spelling mistakes, I am proof-reading but I might still miss something. If you find a mistake would you be so kind to message me about it, so that I can fix it. Thank you.