Bristleback

Rigwarl the Bristleback is a melee Strength Hero whose skills have low cooldown and low mana cost. Although his spells seem very weak at first glance, Rigwarl is a bad hero to underestimate. Quill Spray, Viscous Nasal Goo, and Warpath all provide relatively small effects when used only once, but each ability stacks when cast multiple times. Enemies of the Bristleback will soon find themselves covered in goo and shredded by constant quill fire if they aren't careful. Quill Spray deals increasing damage with each cast on the same target, and due to its low cooldown and mana cost it can be very deadly over time. When Rigwarl sees that his enemies are sufficiently weakened, he can move in for the kill with Viscous Nasal Goo. This ability slows the target and reduces their armor, increasing the damage of Quill Spray and Bristleback's physical attack and making it impossible to escape. Furthermore, casting spells puts Bristleback on the Warpath, which increases his movement and attack damage as he uses his abilities. Bristleback's signature skill, and where he gets his name, is his near invulnerability to attacks that strike his back. All attacks and spells that come from behind him will be heavily reduced and cause additional Quill Sprays. Engaging a strong Rigwarl who is facing away is almost always a pointless exercise.

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.