Retired English teacher Mark Frost, 70, jailed for life after admitting to 45 sexual offences against boys in England and Thailand.
Frost, formerly known as Andrew Tracey, pleaded guilty at the Old Bailey to a catalogue of abuse against nine children in Thailand between 2009 and 2012.
He also admitted having sex with two pupils in Worcestershire over three years in the 1990s.
On some occasions, the abuse happened on school grounds and on others, unmarried Frost's adopted son was present, the court heard.
He was sentenced by Judge Mark Lucraft to serve a minimum of 16 years for each life sentence.
Other determinate sentences were ordered to run concurrently.
Frost raped impoverished Asian boys and encouraged them to engage in sex acts after he groomed them with cash, sweets, computer games and swims in his pool.
Since the allegations emerged in Asia, two former pupils of a school in Worcestershire have come forward claiming they were sexually assaulted in the 1990s. One of them has since died.
Frost had sex with his late victim in a school store room, during breaks, and at his home where he lived with his adopted son.
The judge told Frost he was responsible for "the most appalling catalogue of sexual abuse" and it was clear he had an "ongoing obsession" with young boys.
He said: "Your conduct towards each and every one of these victims is horrific and deeply disturbing."
Additional reporting by PA
