"I saw him, Mr. Fudge, I swear it was You-Know-Who, he grabbed a woman and Disapparated!"
-- Williamson, in the Atrium of the Ministry of Magic after Dumbledore's battle with Voldemort (OP36)
An Auror, who wears scarlet robes and has long hair tied back in a ponytail.
Williamson accompanied Fudge when the Minister arrived at the Ministry of Magic after the Battle of the Department of Mysteries (OP36).
Other canon notes and references
He was probably the scarlet-robed, ponytailed Auror seen in Auror headquarters with his feet up, dictating a report to his quill (OP7).