From the ancient Boxes of Doom™ comes this OIdhammer Minotaur.
I am actually not sure of the name or type code. I think it is Marauder and not Citadel, as the early Citadel Minotaurs had slots for slottabases, while this one has a peg for the later, large 40mm square base like the Marauder. I have not found this in a catalogue though. Whatever the case, I am quite sure this is a Games Workshop model.
Update Oct. 2020: This is by Harlequin Miniatures, “Kurgan Minotaur Blademaster”, thank you Alasdair Robertson for the info!
I used one of my bepoke 3D printed 40mm lipped round bases.
and the comparison.
It looks more like a Beastman champion than a Minotaur when compared to more recent Minotaurs from GW.
Minotaur
Marauder Miniatures (?) GW end of the 1980s
Metal
40mm bespoke 3D printed round lipped base
Painted so far this year: (Miniatures: 192 /365 goal // scenery and terrain: 10)
January: 30
February: 44 // 10
March: 17
April: 45
May: 46
June: 4
July: 2
@The Mountains of Minis 
It is an old Harlequin miniature. It is still available for Black tree design as Kurgan Minotaur Blademaster FA0601.
Thank you for the info! Much appreciated!