The Threarah was the Chief Rabbit of Sandleford Warren. His name in Lapine, threar, means "rowan tree." It is believed he was called the Threarah because there was only one rowan tree in the vicinty of the warren.
He dismissed Fiver's warning to evacuate the warren, and consequently, he is among the many rabbits of the warren who perished.
In the film he wasn't given a name- only credited "The Chief Rabbit". He was played by Ralph Richardson. He is also not mentioned to be Silver's uncle.
The Threarah's role is similar to the book and film where he ignores Fiver's warning and berates Bigwig for allowing Hazel and Fiver to talk to him. He is not mentioned to be Silver's uncle due to Silver being absent from this adaptation. He is voiced by Tom Wilkinson.
In the film, the Threarah was gray furred, old (like in the novel), and rather obese.