Throughout the books, two different Death Eaters named Avery have been mentioned. While it is safe to assume that they are father and son, it has never been confirmed.
The only information known about the older of the two is that he was in Tom Riddle’s class (1938 – 1945) at Hogwarts. According to Sirius Black, the younger Avery was friends with Severus Snape in Hogwarts (1971 – 1978). During the first war he was a known Death Eater but after Voldemort’s fall he avoided Azkaban by claiming he had acted under the Imperius curse. After Voldemort’s return he was punished in book four by a Cruciatus Curse after he begged Voldemort for forgiveness during their reunion in the Riddle House. Voldemort demanded thirteen years of faithful service from Avery and the other Death Eaters before he would forgive them.
In book five he was tortured again, this time for giving Voldemort the false information stating that Broderick Bode could remove the prophecy from the Department of Mysteries when fellow Death Eater Rookwood informed Voldemort that only Harry and Voldemort could remove it. He later participated in the battle at the Department of Mysteries where he was caught and sent to Azkaban. He remains there today.