I am sure those of you who played Oblivion remember Count Janus Hassildor.

And, knowing his true nature, would it not be possible for him to still be active during the events of Skyrim?

Possible. It's also possible he was slain when the Aldmeri Dominion invaded Cyrodiil.

I was thinking along the lines of the vampire guild that you discover in Oblivion may of sniffed him out and did something about it IMHO

The Order of the Virtuous Blood? The three old men sitting in their basemant who admit that they have no skill at fighting vampires and who failed to recognize that their leader was a vampire?

Derp, my bad. I was talking about the ones you have to shoo away from Skingrad. Forgot the quest name http://www.uesp.net/wiki/Oblivion:Information_at_a_Price is what I was thinking of, but I totally forgot the one in the IC My bad!

If Janus Hassildor did not die when the Dominion invaded then He is likely still alive, and possibly a higher ranking member of the College of Whispers. The Dominion are not tolerant of Vampires.

You get rid of that band of hunters for Hassildor. They're either dead or they won't be coming back.

Count Janus Hassildor.

"I WILL NOT AND SHALL NOT SPARE URANUS FOR ANY TRANNIES IN BRUMA"

If Neloth survived both Red Year and the Argonian invasion, I'd say it's not implausible for Janus Hassildor to still be alive.

Very true. I wish he'd been put in the game as an Easter Egg - Oblivion needs some love, too!

This and Neloth is obviously extending his life with magic.