Ajax was a chestnut colt bred by Alfred Thompson and E.L. Balllieu that was foaled in 1934 at the Widden Stud in the Denman, New South Wales area.

He was by the racehorse and sire Heroic, and his dam, Medmenham (IRE), was by Prince Galahad (GB), who won the Dewhurst Stakes.

Medmenham was a race winner in Australia after her importation and was the dam of two other winners in Humorist and Hesione (won AJC Gimcrack Stakes, Maribyrnong Plate and VRC Ascot Vale (2yo) Stakes).

[5] Ajax commenced his three-year-old season by winning the VATC Chatsworth Plate and then the Rosehill Guineas in a new race record time.

In the AJC Derby he was defeated, by a length, by Avenger, to whom he had conceded two stone (12.7 kg).

[6] In the 1939 Rawson Stakes, he started as 40 to 1 on favourite and was defeated by Spear Chief by half a length.

Ajax did not meet with the same stud success in America that he had in Australia, but he did sire Avracado $71,813, Trebor Yug $19,420, and A. Jaxson $11,444.

[10] All this justified Ajax's inclusion in the Australian Racing Hall of Fame in 2004.