I believe it originated in the Skyrim kink meme,brought up by anon.
(all examples are used courtesy of Skyrim kink meme)
'Make it quick;Ulfric's cock is very busy.'
'The Thalmor consider Ulfric’s cock an asset, but they haven’t been in touch with it in a while.'
'Ulfric's cock is so glorious that whenever he comes his cock shouts FUS RO DAH!'