Ragnaros by SaltyPete

Ragnaros is so hot that even the air around him ignites. Wherever Ragnaros moves or casts an ability, he leaves behind a trail of flames that last for 3 seconds and do 30 damage a second when you stand in them. 

Ragnaros smashes down with his legendary mace, Sulfuras, in a cone in front of him after a short delay. The impact does 60 damage, and stuns heroes for 1 second. 10 second cooldown.

Ragnaros' heat can cause even the ground to explode. Ragnaros creates a Magma Trap at the target location after a short delay, which lasts for 5 seconds, and launches anyone who steps on it into the air for 1 second. 15 second cooldown.

Ragnaros launches a fireball that sets the very soul of the first thing it touches on fire. This leaves a damage over time effect that does 80 damage over 5 seconds. 8 second cooldown.

Ragnaros simply being summoned into the world created a volcano, and he can easily do it again. Ragnaros can channel for 5 seconds to form a volcano in front of him that erupts molten rock at units in a wide radius around it once a second, stunning for 0.25 seconds and damaging anyone who gets hit by the chunks. 100 second cooldown.

Ragnaros calls to him 4 Sons of the Flame, fire elementals that will follow Ragnaros and attack whatever he is attacking rapidly for small damage. After attacking 10 times, a Son of the Flame will split into two new Sons of the Flame, each with the same HP remaining as the one they split from. Each Son of the Flame lasts for 15 seconds. 80 second cooldown.