Doctor Aloysius Animo, was once a promising researcher in veterinary science who had a special way with animals. His career was cut short when it was discovered that he was performing twisted genetic experiments on animals. He had hoped that his research would win him the Verties Award, which is an award in veterinary science. Because of the nature of his research, he lost the award to another doctor, named Kelly. This drove him mad, and he dropped off the map for five years until he could perfect his research. In the episode "Washington B.C.", he finally finishes his work, primarily due to seeing the report about Diamondhead saving a campground back in "And Then There Were 10", which pushed him to find a way to create his own "monsters". For some reason, his skin is currently yellowish-green. A picture of him on Gwen's computer shows that he had normal skin in the past.
By using the Transmodulator, a device of his own design, Animo can mutate animals into giant versions of themselves. The second phase of his work involves reanimating dead cells, literally bringing dead animals back to life. All of this is in pursuit of the award which he had lost. His quest ends in failure, since Ben was there to stop him, reversing the effects of his Transmodulator by damaging it. He is arrested in that episode.
He appears again in the episode "Dr. Animo and the Mutant Ray", where he creates a much larger version of the Transmodulator using the broken-off faceplate of the Omnitrix. This version mutates living creatures with alien DNA, creating odd mixtures of alien and terrestrial creatures, such as a "Heatbat". Before he can complete his plans to use a satellite to shoot the ray all over the world, Ben stops him with Gwen's help. Since his mutants were never shown being cured, it is possible that they are still around. For some reason, his trademark giant frog is also present, though he may have simply re-mutated it sometime after his original defeat. How and when he escaped is unknown.
In "Ben 10,000", Animo is still alive, though his head is the only part of him that remains. He had attempted to gain Kevin 11's powers by recreating his mutation. He failed and destroyed his body, but managed to survive by placing his head in a special preservation tank. However, it controls a unique apparatus that allows him to attach himself onto animals specially reformatted with a device (in this case, an albino gorilla) and control them. He was the one responsible for creating Exo-Skull and reviving Vilgax. He is defeated by both Gwen and her future self, Gwendolyn, as well as a cybernetically-enhanced Grandpa Max.
The animals he has mutated or reanimated include a mammoth, a Tyrannosaurus Rex, a bat, a cockatoo, a hamster, a rhino, a seagull, a squid, and his trademark frog. Vilgax could be counted in as one of the creatures since Animo reanimated him. The same goes for Grandpa Max in "Dr. Animo and the Mutant Ray", when Animo turned him into a slug-like creature.
In "Divided We Stand", it is revealed that his first name is Aloysius. He escapes what seems to be Alcatraz Island on a mutant seagull and captures one of Ben's Dittos to access the DNA stored in his Omnitrix. He creates an army of self-replicating Lepidopterran mutants, but they were soon destroyed, and he was captured again.
He makes a brief appearance at the end of "Goodbye and Good Riddance", wearing an ape-like exo-suit, and leading a group of animal mutants towards Ben's school.
He appears in "Ben 10 vs. The Negative Ten (1)", as part of the Negative 10, but since he was working with Clancy he has learned ways to gain psychic control over animals, and he uses this new ability in Ben 10: Secret of the Omnitrix (Secret of the Omnitrix was set between episode #52 and Race Against Time, even though it aired before both), where he uses an invention called the DNA Bomb to try to de-evolutionize the world. Fortunately, Ben using Heatblast (in other versions of the movie, XLR8 and Eyeguy) to overload the system and cause an error at the last 2 seconds, but because of this it triggered some waves to hit the Omnitrix and set it to self destruct as he makes his escape. Later on, he is defeated by Greymatter though.


Doctor Animo's Mutants
Dr. Animo has made seven appearances in the Ben 10 Series.

Doctor Aloysius Animo's First Appearance
Washington B.C.

Doctor Aloysius Animo's Last Appearance
Goodbye And Good Riddance