What counters bruisers?

As an archetype of a champion design. Sure you have count champion designs, but a mage, marksman, assassin, and tank. They all have fairly well defined counters to what that do. Mages and Marksmen tend to lose to assassins, assassins lose to tanks, tanks loose to mages and marksmen. It's more or less the whole rock, paper, scissors aspect of the game people love to talk about but normally don't actually understand.

Bruisers are by design somewhere in the middle of the other three, although by doing so what counters a tank that's enough of an assassin that marksman and mages can't beat him? Or an assassin who does enough sustained damage that a tank can't absorb their damage output? How are you suppose to beat a champion who is designed in a way which has no counters, excluding another bruisers designed with a counter mixed archetype.

Something needs to be done in terms of items, stats, or even if it means completely reworking a good number of champions, to address these imbalances in the basic structure of the game's design.

So again i return to the initial question, what is the counter to the bruiser/fighter archetype?