He's an American living in Paris, 5600 miles from his partner in Sunn O))), the heaviest band on the planet. He's a compulsive musical collaborator, wreaking eldritch, entropic tones from his Travis Bean aluminium-necked guitars. He devises a seemingly endless slew of album covers that elevate acquiring the vinyl they envelop to the status of ritual. He even runs an imprint, Ideologic Organ, through which he issues specialist recordings alongside his own experimental projects. He's a "gear freak" too, he confesses down the line from his apartment just north of Pere Lachaise cemetery, where he moved from New York in 2007.
But don't call him a metalhead, a common misconception among those for whom O'Malley's role in Sunn O))) - whose mesmerisingly nebulous scope takes in drone, metal, musique concrete and classical contemporary music - marks him down as a pillar of the genre.
"I've never felt part of the black metal scene, even though I have a lot of friends in that scene and like a lot of the music," he says. "I played in metal bands when I was younger, and it's just a different way [of playing guitar].
"It's not better or worse - it's different. I like metal as much as raga music, and I like raga music as much as Japanese flute music. I like sound. I like music that invigorates me and that has to do with the attitude of the music, not the virtuosity of it."
Lest O'Malley come across as po-faced, he laughs riotously when I suggest the group he's most associated with are best listened to while braising meat and drinking glutinous red wine. "That's a great way to put it - it's part of a feast, an extravagance," he says brightly. "Sunn O))) is not an everyday thing, for sure."
Besides Sunn O))) - pronounced "sun" - the 42-year-old's projects include the duos KTL (eerie ambience) and ÄÄNIPÄÄ (mutant tech-noise) plus trios Nazoranai (avant-rock) and Gravetemple (doom), not forgetting the cosmic pulse of Ensemble Pearl and Shade Themes From Kairos, his forthcoming album with longtime collaborators Randall Dunn and Oren Ambarchi, the Australian multi-instrumentalist who mans the kit in Nazoranai and Gravetemple.
It is as a solo artist, though, that O'Malley will next face his Scottish disciples, when he kicks off a week-long UK tour with his friends, French occult rock trio Aluk Todolo, in Glasgow. He's looking forward to the change of discipline. "I love playing music with others, and that's the pleasure of music for me. That collaborative communication, the camaraderie around it, the vested risk you are all taking is really exciting. When it goes well it's rewarding.
"When you are playing solo you don't have that. It's entirely different. I'm not playing songs, though. I suppose it's different for a songwriter, and someone who has more song structures. I'm playing something that's a 45-minute piece. I've got to admit I use it as a sort of self-analysis." He chuckles.
The visit to Glasgow marks O'Malley's third in 12 months, the first to participate in the second Tectonics festival (the first took place in Reykjavik) and the other with Nazoranai - Japanese avant-rock figurehead Keiji Haino completes the three-piece - last summer.
"I was contacted by someone at the art school," he explains, "and they're like: do you wanna do something? And I'm like: do you know I've been in Glasgow twice in the past year? And they said: we don't care." Another wave of laughter. "So we put this trip together with Aluk Todolo. They're a great band, they have three or four amazing albums, they tour a lot in places like Romania and Poland but they have never had a chance to tour the UK."
O'Malley owes his appearance at Tectonics - his multiple performances included the dual-guitar minimalism of Alvin Lucier's Criss-Cross with Ambarchi, Metalstorm II with Ana Maria Avram and the weekend's closer, his guru Iancu Dumitrescu's appropriately seismic Hazards And Tectonics - to its co-curator Ilan Volkov, the former chief conductor of the BBC SSO.
Volkov also enlisted O'Malley's services in Adelaide last month for the inaugural Australian iteration of the eclectic shebang.
Curiously for those infatuated with Sunn O)))'s last album proper, Monoliths And Dimensions, O'Malley suggests Volkov played a part in that record's drift into orchestral territory, as did the American composer and instrumentalist Eyvind Kang, whose arrangements add a transcendental undertow to such tracks as Alice.
"That album may have been a little inspired by my relationship with Ilan," he says. "We share a lot of information about composers and other things the other might not know about, mainly in my direction. He's got a f****** astounding memory.
"But also Eyvind Kang did a lot of the arrangements on Monoliths …, and he and Ilan have done some pretty cool projects. They did some concerts for the Iceland Tectonics, pieces written by Eyvind and Jessika Kenney - they are husband and wife. And Jessika is also on Monoliths. She's an incredible singer."
For now, though, O'Malley is content to step away from what he calls his "little solar system of people". "I appreciate having the opportunity to do something solo and consider things in that way, and have an audience who are interested. It's a real gift."
Present intense? You could say that.
Stephen O'Malley plays Glasgow Art School on Tuesday, April 8.