John Oliver has, in the past year or so, become the conscience of the American media - once again taking up a mantle he held extremely well while covering for pal Jon Stewart on The Daily Show.

His HBO show, Last Week Tonight is one of the biggest recent success stories of talk television, and crucially, it's produced on his own terms.

While some have called it a weekly rant, what essentially you have is someone believing in something, or against something, and using his given platform to inform on whatever issue it may be. Simple, really. 

This week, it was once again the American prison system. Calling it flawed would be an understatement.