Do you mind giving your reasons for thinking that?

Varieties of Faith in the Empire mention Cyrodillic legends of Magnus inhabiting the bodies of Archmages, and mentions Zurin Arctus is associated with him. Since the legend comes from Cyrodill, and he is most likely one of the mages in the legends, then he would likely be a Cyrodill.

A la Shezarr, or HoonDing? Or something else entirely?

I don't know.

Since Magnus is much more whole than Akatosh and Lorkhan, I imagine it is pretty much flat-out possession.

Zurin really isn't an Imperial name, though. The Underking has red eyes, and Zurin Arctus sounds more to me like a Dunmer name than anything else. Kind of makes a certain sense, given the previous owners of the Numidium.

The legend comes from Cyrodill but that doesn't mean Imperials are the only ones he can inhabit. I think its just as likely Magnus would go for cultures that actively prey to him which Altmer and Bretons do.

By your logic Ysmir, the most resent Dragonborn, can only be a Nord and the Nerevarine can only be Dunmer. And we know that's not the case.

These eyes look gold to me. [img]http://images.uesp.net/f/fd/DF-Underking_Face.png[/img]

No, then he'd be Arctus Zurin.

Besides, there's really no hard and fast rules for Cyrodiilic names. Also, Arctus means 'Bear' in Greek (okay, Latinized Greek, but that's not the point).

Dunmeri names only put the Great Family names prior their given and sur names, so it is still Zurin Arctus if he's a Dunmer, only Hlaalu Zurin Arctus or Telvanni Zurin Arctus or others.
And he still seemed elven to me, at least before Wulfharth ripped his heart out, though which race was debatable. Lorkhan loves the whole Mundus, so the Shor-Wulfharth-elf-hater needs a Elf-Zurin-Arctus to balance, and inbetween was Hjarti-bretonish-nord-who-is-mixed-all-around.

I also feel that it's unlikely that the Grand Battlemage in late 2nd era Cyrod would be a non-man.

Remember, all that multicultural hijinks with Altmeri Battlemages and Dunmeri Counts doesn't get started until after the Septims are in power.

Vanus Galerion was an Altmer and he left Artaeum to build the Mage Guild, and eventually came to the mainland in pursuing Mannimaco, who was also an Altmer.
It can be safely assumed that in the early stage of Mage Guild most members were Altmer. And as Mage Guild developed in the mainland, Altmer mages kept moving to the mainland. And it seems logical that some of them contributed to the development of the Cyrod battlemages...oh well, maybe Zurin Arctus was one of them?

And also Vanus Galerion had a surname...or maybe it can be called a surname? If not, why Zurin Arctus was not like it?

Interesting. Never thought he could have possibly been a Dunmer. I always thought he'd been a Cyrodiil.

Symmachus was a Dunmer and a General of Septim. Maybe it wasn't that hard (or wouldn't have been) for an elf to rise to the Imperial Battlemage position.