Voldemort was never given a reason to become an Animagus. We know his greatest desire is to be immortal, and being an Animagus would not help this. On the other hand, being an Animagus would not give him any special power in clearing his way to immortality. Killing curse is usually enough for him.
No, Voldemort was not an Animagus. He didn't see any reason to become an Animagus despite being a gifted wizard and knowing a lot of magic. This may simply be because his sole purpose was to obtain immortality and become the strongest wizard who could control the world around him.
Fandoms: Harry Potter - J. K. Rowling
Harry likes hamsters. What a coincidence that Tom is a hamster animagus.
“A creature I wouldn't want to kiss . . . a spider!” Harry figures out the riddle, and realizes that a spider is about to attack. But what he doesn't realize is what I now believe: that the spider in the maze is Professor Snape, in his Animagus form. It is Spider/Snape who bears down on Cedric and Harry.
As a pack animal, or as a “lone wolf,” the wolf is a perfect fit for Harry's Animagus form.
They are James Potter, Sirius, Wormtail, Skeeter, McGonagall, Talbott Winger, and an unnamed witch who can turn into a cat. The fact that there are so few Animagi just causes us fans to want to know more about them.
Peter Pettigrew's Animagus form was a rat. Colloquially, a "rat" is a snitch or informant. Webster's also lists the following possible definition: "a contemptible person: such as... one who betrays or deserts friends or associates."
Hermione (Raccoon) - very curious, and enjoy inspecting and examining everything. They are also known for high intelligence.
A teacher who taught the skill did not need to be an Animagus themselves, as shown when Professor Dumbledore, who was not an Animagus, taught Minerva McGonagall how to successfully become one.
At the end of GOF only a handful of people even know that Sirius is an animagus, let alone his loveable big doggie form. But by the beginning of OOTP we have Lucius Malfoy able to "recognize" Sirius by seeing the large black dog with Harry.
Lily was an animagus too, when Voldemort attacked, she transformed in front of him so that she could attempt to escape. Voldemort hit her with a spell which locked her in her form as a twisted way of leaving her alive for Snape. Harry never noticed but there was always an animal watching him as he grew up.
Draco's boggart would likely be in the form of the Grim Reaper with young Malfoy's own face under its hood. Surprisingly, Lord Voldemort was not Draco's greatest fear.
Nymphadora Tonks, who we first meet in Harry Potter and the Order of the Phoenix, is a Metamorphmagus. She tells Harry that the ability helped her greatly in the Concealment and Disguise in her Auror training.
For example: if Viktor Krum can transfigure his head into a shark's, like he does in Goblet of Fire, that doesn't mean he is an Animagus. Transfiguration is a form of spell-casting, whereas becoming an Animagus is forever. And yes, he could turn into a falcon.
Did Dumbledore know the Marauders were unregistered animagi? No, he didn't until very much later. James, Sirius and Peter turned themselves into Animagi without the knowledge of the wise old headmaster.
James Potter
James's Animagus form was that of a stag, which earned him his nickname, Prongs. Strikingly, Harry's Patronus was a stag and his mother Lily's was a doe, a female deer, showing that the family's characters were in harmony and formed part of the same animal group.
Sirius's early life proved unhappy; he had come to hate most of his relatives, in particular his mother. He rejected his family's pure-blood elitism and reverence for the Dark Arts. At Hogwarts, rather than be sorted into Slytherin like the rest of his family, Sirius was placed in Gryffindor.
Because there was no need for him to become one. Besides he had lot of other important stuff going on in school unlike his father and his friends who were determined to help Lupin.
Harry discovers this in Prisoner of Azkaban, when his Patronus turned out to be a stag, his father's Animagus form.
Summary: Basically, I read a fic (The Houses of Pendragon, Emrys and Potter), and in this fic, Merlin's animagus is a black dragon.
Falco Aesalon — Falcon; the first recorded Animagus; the registration system was not in existence in his time.
…in Transfiguration and Potions at least. Becoming an Animagus requires a witch or wizard to be skilled in both these areas in order to stand a chance of achieving such a complex transformation.
At Hogwarts, she, along with her sisters, was sorted into Slytherin. It is suggested in the novels that, as a student, Bellatrix associated with a group of students – including Rodolphus Lestrange, Severus Snape, Avery, Evan Rosier and Wilkes – who nearly all became Death Eaters.
Talbott Winger was a wizard who attended Hogwarts School of Witchcraft and Wizardry in 1984 and was Sorted into Ravenclaw house. He was also an Animagus and took the form of an Eagle.
Maledictuses could transform into animals like Animagi, but were very different: unlike Animagi, they lost the ability to think like a human over time, and they transformed due to a curse, while Animagi had to transform through a potion and through a tough ritual involving the potion.