Marshal Reginald Windsor was a human knight of Stormwind who discovered that Katrana Prestor was really the black dragon Onyxia. He was instrumental in unmasking her, though he paid for it with his life.
Marshal Reginald Windsor was a legendary knight and commander in his best days. He was a loyal friend of Varian Wrynn and studied swordcraft with him, although Windsor came to favor the hammer. With nerves of thorium and wielding his family's epic hammer Ironfoe, he became a living legend in Stormwind. Later he was assigned the post of the commanding officer of Alliance forces in Burning Steppes. Apparently, he traveled to the Burning Steppes to investigate the Dark Horde and obtain proof of Lady Katrana Prestor's treachery for Highlord Bolvar Fordragon. However, when a flippant King Varian Wrynn returned to Stormwind, Windsor was troubled by Varian's passiveness and began investigating the possibility that an impostor — possibly even a dragon — had taken the king's place.
As threats of Blackrock orcs grew, he and his agents traveled to Blackrock Mountain to investigate. While traveling with the information they gathered, his squadron stumbled into a Blackrock orcs battalion laying traps for an upcoming battle with the Dark Irons and were forced to fight them. Though Windsor managed to defeat the orcs, he was spotted by 300 Dark Iron dwarves and was captured. Only one of his men, Ragged John, escaped telling the tale. Marshal Windsor was captured and imprisoned, his hammer taken by the Emperor, Dagran Thaurissan, and the precious information seemed lost.
Eventually, however, he was rescued by Varian Wrynn, Broll Bearmantle, Valeera Sanguinar, and Thargas Anvilmar. He revealed to them the dark secret that he learned while stationed in the Burning Steppes: that the court of Stormwind had been infiltrated by the black dragon Onyxia, in the guise of Lady Katrana Prestor. Reginald Windsor accompanied the four to Stormwind and, even though he knew it would lead to his death, he confronted her, revealing her true form within Stormwind Keep. With her plans unraveling and her disguise ruined, she incinerated Windsor and escaped to her lair.