Bristleback

Rigwarl the Bristleback is a melee Strength hero famous for his array of synergistic spells with low mana cost and cooldown. He is able to slow his enemies down and reduce their armor with Viscous Nasal Goo, then hit them with a barrage of Quill Sprays, making him an effective chaser when ganking enemies. His low strength gain makes him less tanky than most strength heroes, but he becomes exponentially more durable when he turns around due to his passive Bristleback, which reduces damage taken from behind. In the right hands, Bristleback is a powerful ganker in the early stages of the game, and a powerful semi-carry in the later stages depending on how much farm he gets.

Trivia

 * Bristleback has the highest intelligence gain per level of any hero whose main stat isn't intelligence.
 * In DotA, Bristleback gained notoriety for his high effectiveness in competitive play; several high-level tournaments banned Bristleback play entirely.