Harness racing legend Courage Under Fire has died at the age of 21 at Yirribee Stud in NSW.

The diminutive New Zealander, known as Mighty Mouse, was unbeaten at two and three, winning his first 24 starts and a record six Derbys.

In all, he won 41 of his 56 starts before he was retired to stud.

His most successful progeny was the recently retired dual Inter Dominion winner Smolda.

Credit: AAP