"There's nobody that I've ever known, ever, that's risen to the presidency that was actually of evil character," he told CNBC's "Squawk on the Street." "Anybody who attacks people in the manner that he attacks people … that's evil."
Soon after Trump swept to a strong victory in Indiana on Tuesday, his two remaining opponents — Sen. Ted Cruz of Texas and Ohio Gov. John Kasich — suspended their campaigns. With no one standing in his way, Trump ascended to the status of presumptive Republican nominee.
Diller is also a supporter of Democratic front-runner Hillary Clinton.
In the same interview, Diller, Expedia's chairman, said he was optimistic the travel giant would survive the rise of start-ups like Airbnb and HomeAway.