In the book
The book tells the story of Horton the Elephant who, in the afternoon of May 15 while splashing in a pool located in the Jungle of Nool, hears a small speck of dust talking to him. It turns out the speck of dust is actually a tiny planet, home to a city called Who-ville, inhabited by microscopic-sized inhabitants known as Whos and led by a character known as the Mayor.
The Whos ask Horton (who, though he cannot see them, is able to hear them quite well, due to his large ears) to protect them from harm, which Horton happily agrees to do, proclaiming throughout the book that "even though you can’t see or hear them at all, a person’s a person, no matter how small." In doing so he is ridiculed and forced into a cage by the other animals in the jungle for believing in something that they are unable to see or hear. His chief tormentors are Vlad Vladikoff, the Wickersham Brothers and the Sour Kangaroo. Horton tells the Whos that, lest they end up being boiled in "Beezelnut Oil", they need to make themselves heard to the other animals. The Whos finally accomplish this by ensuring that all members of their society play their part. In the end it is a "very small shirker named JoJo" whose final addition to the volume creates enough lift for the jungle to hear the sound, thus reinforcing the moral of the story: "a person’s a person, no matter how small."
Now convinced of the Whos’ existence, Horton’s neighbors vow to help him protect the tiny community.
In the Movie
In the movie, the Sour Kangaroo hires Vladikoff to attack Horton and destroy the clover he is carrying (the clover that holds the microscopic city of Who-ville).
Vlad Vladikoff is voiced by Will Arnett. He is the vulture in the scene where he tries to get the clover. There is a confusing matter about a good Vlad is a rabbit (which bakes cookies) and a bad Vlad. Vlad is a reclusive vulture who lives in a tree stump in a swamp surrounded by thorns, feasting on a zebra carcass. The Sour Kangaroo hires him to get rid of Horton's clover. At first, he agrees to do it in exchange for a brand new pair of objects never specified beforehand, but he stated her son Rudy. After "thinking" it over, she uses reverse psychology to get him to do it for free. He speaks in a thick Russian accent and is extremely theatrical in his wickedness to the point of embarrassing himself. He finally manages to get rid of Horton's Clover, but after Horton sucessfully found it, the Sour Kangaroo becomes mad at him and calls him an "IDIOT!".
At the end, Vlad Vladikoff is touched by the beauty of Horton befriending Sour Kangaroo.
In the TV special
In the Chuck Jones cartoon, he goes by the alternate name of Whizzer MacWoff.
Despite being described as a vulture, Vlad actually looks more like a condor.