Mazer Rackham is a character in Orson Scott Card's Ender's Game and mentioned in other books in the series. A "twice court-martialed, half-Maori New Zealander," he is the commander who won in the Second Bugger Invasion for Earth, several decades before the book starts, destroying the entire invading alien fleet by, through luck and a good hypothesis, destroying the ship that held their queen. (Card's script for an Ender's Game movie, at http://www.frescopictures.com/movies/ender/script.html, has Rackham firing on the queen's ship against the orders of his superior.)

As the leaders of Earth know there will be a Third Invasion, Rackham is sent out in a ship approaching the speed of light, so that while fifty years will pass on Earth, only eight will in his ship. (His family have died by the time he comes back.) On his return, Rackham gets to train the next commander of Earth's forces, Andrew "Ender" Wiggin. He's not gentle about it, as the fate of humanity probably rests in Ender's hands:

"When you can give me back my dead wife, Ender, then you can complain to me about what this education costs you."

"Early to bed and early to rise, makes a man stupid and blind in the eyes."

"There is no teacher but the enemy. No one but the enemy will ever tell you what the enemy is going to do. No one but the enemy will ever teach you how to destroy and conquer. Only the enemy shows you where you are weak. Only the enemy tells you where he is strong. And the only rules of the game are what you can do to him and what you can stop him from doing to you. I am your enemy from now on. From now on I am your teacher."

There is also a band called Mazer Rackham, who have a site at www.mazer-rackham.com and describe themselves as "Psychedelic Celtic Folk Punk Rock."