This wealthy Irishman is many things at Celtic: power, influence, mystery, a benefactor to a degree. Desmond is also, at times, meddlesome.
Does anyone really doubt that going for Keane as Celtic manager was a singular passion of Desmond more than anyone else - and probably without the full approval of Celtic CEO Peter Lawwell?
It is seven years since Keane was last a success in football. In his five seasons as a manager, one was a success and four were failures.
He was an eccentric target by Celtic. Given this track-record, if you weren't called Roy Keane, you wouldn't have been considered for the Parkhead job in the first place.
Desmond is a charming bloke, who combines a successful business career with a lifestyle often akin to a sybarite. Yet quite a few Celtic fans are frustrated by his role around their club.
Some believe Desmond could dip into his vast private wealth more than he does on behalf of the club. Other fans view their single biggest private shareholder as a distant figure, a kind of "absent landlord" who should be around Celtic far more than he is.
That last criticism withstands scrutiny only to a degree. These days geography has little to do with proximity. Desmond is living proof of it.
He is certainly hands-on at Celtic - but very much via diktat from a distance. If Neil Lennon said it once he said a hundred times: "I've spoken to Dermot on the phone." Or: "I've got to go to see Dermot."
There is no doubt at all about who the ultimate powerbroker at Celtic is. Desmond loves the club but he remains a mysterious, elusive figure whom few - this writer included - really get to know or understand properly.
His keenness to land Roy Keane for Celtic was one more chapter in a sometimes imperfect marriage between Desmond and Celtic, causing further frustration among supporters.
It became very obvious in recent days that a large section of Celtic fans were Keane doubters - with his patchy record in management, they just didn't see the merit in going for him.
That said, such cynicism was countered by the view, right or wrong, that what Desmond wants for Celtic, Desmond usually gets. In the end it took Keane's own reservations about taking the Parkhead job to bring the saga to a close.
The Keane rejection has left Celtic facing up once more to a harsh truth about the club these days. Which is to say, the prestige around Celtic is badly tarnished by the football environment in Scotland.
Keane called Celtic "a fantastic football club, one of the best in the world". None of this outlook, however, caused him - a man in a part-time role with the Republic of Ireland who craves being a no.1 again - to actually want the job as manager.
Why? Because Keane would baulk at the domestic limitations of Celtic playing in Scotland, let alone the pitiful budget the club is forced to adhere to.
It has been sobering for Celtic - a club run extremely well, and fairly, and with a huge worldwide support - to be treated like this.
In Scottish football, so-called prestige and reputation are one thing. Reality, with its sharp bite, is obviously something else.
All the other candidates for the Celtic job - Steve Clarke, Malky Mackay, Owen Coyle and more - will harbour reservations about taking it. Being out of work, in fact, right now appears to be a prerequisite.
This is nothing new. As much as Gordon Strachan is rightly lauded as a past Celtic manager, the truth is that, back in 2005, Strachan had been unemployed for 16 months and was hardly being chased by big clubs when Celtic offered him the manager's job.
There will always be prospective Celtic managers out there. But the job lacks the lustre it once had.
Not even Dermot Desmond can change that. Only through "environment change", as Peter Lawwell once put it, can Celtic FC realise its potential