Sejuani was first announced by Ezreal in one of his posts.
Sejuani's title was formerly "The Winter's Claw," but has since been changed to "The Winter's Wrath."
Sejuani is likely the anticipated female boar-themed champion, though many thought that the boar would be the champion herself rather than being the mount of the champion.
Sejuani's boar is named Bristle.
Riot employees jokingly calls Bristle as Kevin Tuggles.
In Sejuani's Art spotlight, the artist names the layer that has the boar on it "Piggles". Screen capture of it.
Regarding the Ranca_Golden_Hour speculation, this screencap, from the Art Spotlight at around 5:17 for a split second, it can be seen that Ranca_Golden_Hour.jpg is in fact just a reference image. Google Imaging Ranca Golden Hour will also give this image as the first result.