The 33-year-old "Lost" star told MTV News that he first met Eminem in Paris in a time "before iPods" when a friend handed him a bootleg cassette copy of The Marshall Mathers LP.
"I was completely blown away," he said. "It was one of those moments in music like the first time you hear DJ Shadow or the Beatles. It was a real breath of fresh air."
A self-described "big rap fan" (old-school stars Rakim, Public Enemy and KRS-One are among his faves), Monaghan said he was drawn to the album, playing it over and over because Eminem touched on topics not usually covered by rap artists.
"I was used to rappers shoutin' at me about people they've killed, and here Eminem was rappin' about Vicodin and tripping people out at late-night parties. It was a voice I'd never heard before," he said.
"Songs like 'Kill You' and 'Kim' were just insane," he added.
Monaghan also said he admires Eminem's anger-management skills — a sentiment rarely heard about the MC. "He has a very good handle on his anger," Monaghan said of Em, who was once arrested for starting a bar fight after one of his wife Kim's male friends kissed her on the cheek. "He's able to channel it very easily. Instead of hiding behind it or pretending that there's something else going on, he actually is able to pinpoint where his anger is coming from."
In "Love the Way You Lie," Monaghan plays the angry husband to Megan Fox's fighting-mad wife. The volatile couple's passionate relationship blossoms, then violently crumbles within the vid's four-minute span. It is a relationship said to be symbolic of that of Eminem and Kim, the ex Em married and divorced twice.
In order to play a version of Eminem in the video, Monaghan says he asked Eminem's manager a ton of questions then he simply "led with anger." The actor did not talk to the MC himself because Eminem shot scenes two days before Monaghan and Fox arrived.
"We didn't cross paths," he said.
Is "Love the Way You Lie" among Eminem's best videos? Talk about it in the comments!