'Berwick, the Witch Hunter is a custom champion in League of Legends.
Berwick (pronounced Berr-ick, very similar to Warwick) is intended to be the terror of mages everywhere, and a good hard counter to very heavy AP teams. With tons of MR, a medium cooldown powerful AOE silence and an ult that scales with enemy AP, he's designed to shut down and chase after mages, finishing them off with strong autos.
Itemising for him is interesting, I think. He lends himself to bonus movespeed so he can chase effectively, and he benefits nicely from Tenacity, reducing CC effects to only a third in combination with his E, and attack speed would scale well with his ult, so Zephyr would be a particularly nice item for him. Mercurial Scimitar gives him the AD and MR he wants, whilst giving him a cleanse so he might use his E on a squishier teammate to prevent assassinations, though with all his tenacity, it might be a little superfluous. Guardian Angel allows him to throw himself into a fight and fare acceptably even against AD opponents such as the enemy ADC. Resource management will be important for him, though, as there are few to no appropriate mana items for him to build, Chalice and its build paths being weak on him and Manamune ruled out due to the difficulty of stacking it.
He'd be at home in toplane against APs, though he might have a hard time against certain champs like Kennen who rely on AD early on for poke, what with his lack of innate sustain. I think he could also do well in midlane against the mages who typically reside there, as his Q, if well timed, should be a pretty effective tool at shutting down ganks.