The ‘Wheel’ we can see in these two
pics are a wind turbine thingy, I think. And if the wizard is on a white horse, it’ll be Gandalf.
This is from the chapter The Seige of Gondor:
“In rode the Lord of the Nazgul, under the archway that no enemy ever yet had passed, and all fled before his face. All save one. There waiting, silent and still in the space before the Gate, sat Gandalf upon Shadowfax….”
Plus the white horse has no bridle or saddle, which is how Gandalf rides him.