Lenny Yogman (voiced by Josh Peck) and Denny Yogman (voiced by Austin Stout), often known collectively by the Yogman Twins, are fraternal twins that are rarely seen attending class. Instead they are in the laboratory located in the school's H.V.A.C. system. They wear red hats that resembles the 1980s band Devo's energy dome hats, yellow shirts, and black sneakers. Lenny is the taller twin and Denny is the shorter twin. They have occasional victories and occasional defeats. When defeated, they end up hissing much louder than they normally do. In the Robot Jones promo, the Yogman Twins are said to be among the antagonists with the mission to destroy Robot Jones. They’re a pair of bullies that often sneak up on the main characters. They target Robot more than any other character. In "Cube Wars" it’s revealed that Lenny and Denny share the title of Wondercube World Champions. Denny has a higher voice than Lenny. They finish each other’s sentences. When speaking to each other they refer to each other by using the word "Brother".
Lenny and Denny are mainly almost the same. They are very imprudent, malicious, crafty, cruel, charismatic, mysterious, childlike, manipulative, creepy, untrustworthy and rude. Lenny is the more talkative one out of the twins and is presumably the eldest brother.
Lenny can be critical towards Denny if a plan is failing to succeed. Lenny often bosses his brother around and he appears to be slightly more cruel than Denny, showing little remorse towards the characters.
Denny is very loyal towards Lenny and is happy to play along with his horrid schemes. Denny appears to be the more redeemable one of the twins but chooses to remain bad-mannered. He sometimes shows his true emotions then quickly reverts back to his usual self.
- Greg Miller stated that Lenny and Denny were inspired by Tweedledum and Tweedledee from Alice in Wonderland.
- Their early designs in Greg Miller's sketchbook show Lenny and Denny as having very identical bodies to Tweedledum and Tweedledee. They also have brown hair instead of black hair.