Board Thread:Naruto Discussions/@comment-16064415-20140829133523/@comment-1411686-20141008233409

Ten Tailed Fox wrote: How do we know Yagura wasn't Mizukage then? We don't even know his age, when his reign began, or when it ended. We do know that Mei stated that it became the "Bloody Mist" under the reign of the Fourth Mizukage, which is Yagura.

Edit: And if your answer is related to Isobu, keep in mind, we neither know how old he was when the beast was extracted from him, nor when it was sealed within him. All we know is that, at some point, he was its jinchuriki, and at some point, he lost it.

Except we saw Yaguras true personality was very benevolent; so its obvious he didnt start the Bloody Mist.