Filling Ozzy Osbourne’s shoes wasn’t exactly the easiest of ventures. Yet, amid the fiery whirlwind of Osbourne’s legacy, his value to Black Sabbath lost its focus. While the band had always been a leading force in rock, with a somewhat erratic captain at its helm, they needed a fresh, dynamic presence at the eleventh hour. Ronnie James Dio would be the only man for the job.

Anyone would have felt daunted by the idea of replacing such an irrefutably legendary figure in metal, even if he simultaneously became a laughingstock among his peers. But Osbourne’s idiosyncracies are a part of his reputation, his fearlessness in doing something as objectively absurd as snorting a trail of ants seemingly matching up with his aggressive pursuit of musical greatness.

In response, Dio joined a long list of people astounded by Osbourne, though not enough to find him truly intimidating. “Replying to the things Ozzy has said to me is like duelling with an unarmed man,” Dio comically quipped during a radio interview in the 1980s. Dio wasn’t trying to be Osbourne’s carbon copy, and he celebrated their differences, mostly because he regarded Osbourne as lacking intelligence.

“I really feel like someone who has a sword up against someone who just has no clue what a weapon is,” he explained, taking a serious jab at the former frontman. “I find the man to be stupid, totally devoid of intelligence, an animal, and I could give you examples of all these things to back up what I’m saying. I would not say them unless I firmly believed these things. And I wouldn’t say them unless I felt that at some point someone need reply to moronic statements that Ozzy has made about people who, let’s face it, made him all the money in the world.”

Dio’s honesty earned him a lot of respect among rock and metal groups, mostly the ones who value musicians who say it as it is—with little regard for how their words or delivery might land in the recipient’s ears. While he was performing alongside Deep Purple, for instance, he recalls getting to know Ritchie Blackmore on a personal level, but the lessons he learned might not have been as positively profound as you might expect.