MacGregor was a Manticoran citizen and sport fisherman.
In the 1920s PD, he was fishing for Bahamut fish near an island less than two thousand kilometers above the southern ice pack of Sphinx when he caught sight of an unknown group of treecats on the island. He headed in immediately, but by the time he landed the treecats had disappeared. He subsequently notified Doctor Adelina Arif of his discovery, prompting her to make a rapid flight to the island with six memory singers and two dozen scouts and hunters. (HHA8.5: CSS)