General Mono was part of a brotherhood formed by his brothers and sister to conquer the world. During the brotherhood's existence, Mono's brother Yaotl discovered a constellation known as the Stars of Kikin which would align every three-thousand years to open a portal to another dimension. During a battle between Yaotl's army and a Central American civilization, Yaotl used a wheel-like object to open the portal, but had a cost: Mono, along with two of his brothers and sister were turned to stone, and thirteen monsters were summoned to Earth. The monsters quickly wiped out both Yaotl's army and his opponent. Yaotl himself was left cursed with immortality.
Three-thousand years later, Mono and the other Stone Generals were reanimated by Yaotl (under the alias of Max Winters) and Yaotl made them capture the Thirteen Monsters assisted by the Foot Clan. They captured twelve of them and captured Leonardo as a replacement for the thirteenth monster. Later, Mono and his brothers and sister led by his brother Aguila turned against Yaotl, thinking he would take their immortality for himself. Yaotl, however, was trying to get rid of the immortality by casting the thirteen monsters into the portal. During the next alignment and reopening of the portal, Mono and the other generals revealed their intentions to summon more monsters to Earth to use as an army to finish the world conquest they had started three-thousand years ago. The four turtles led by the rescued Leonardo then confronted the generals. During the fight, General Mono engaged Donnatello in combat. The 4 turtles barely defeated the stone general and kicked him into the portal. The stone generals emerged from the portal and Aguila stated that they would never be vanquished without the thirteenth monster. Just then, the thirteenth monster barged into the room and slammed the stone generals and itself into the portal. Mono and the other stone generals were turned human again in the process, apparently breaking the curse.
The poise and the look itself already gives a trembling fear to anyone who battles this general. General Mono's bulky body matches up with his weapon, his hammer. With his hammer and his incredible strength he can create waves that blows anyone near him whenever he slams the ground plus, his powerful legs can lift his very big body into the air and pounds the ground, slamming heavily to anyone under his feet. But even this tough guy has his weakness, that is his slow movement.
- Mono was the only general not to have a speaking line, but speaks in a 1960's Hulk-like fashion in the video game.
- Mono means 'monkey' in Spanish.