Stormwind Gryphon Rider

Stormwind Gryphon Riders are squads of mounted human soldiers atop their trusty white gryphons in Stormwind City. One can find 2 squads: In the Trade and Military districts, and near the palace. If you get to close to them as a Horde player, they'll chase after you like mad.

During the Battle for the Broken Shore, many of them accompanied the third fleet to the Broken Shore. Most didn't survive.

Speculation
They may be a part of the Stormwind City Guard.