Invincible episode 4 teases Robot's plan and how Rex Splode plays an important part. Amazon Prime Video's animated superhero series based on Robert Kirkman's comic is already halfway through its first season. While the focus is on Mark Grayson's origin and the big Omni-Man twist, the show also has introduced a plethora of characters to fill out the world. In many cases, these supporting characters will go on to have important roles to play in Invincible's future.
One of the most mysterious characters early on is Robot, the former leader of Teen Team and current leader of the new Guardians of the Globe roster. Invincible episode 4 repeatedly sets up that something isn't quite right with Robot. He's monitoring the only Mauler Twin currently alive and takes a sample of Rex Splode's blood without him knowing. The episode ends with Robot offering this blood sample to a disfigured human inside a containment chamber. All of this plants the seeds for Robot's true plan in Invincible.
Robot's plan in Invincible is to create a new human body for himself. The disfigured person Robot approaches at the end of Invincible episode 4 is his original human body. He is named Rudolph 'Rudy' Conners in the comics and appears this way due to normal air serving as a poison to him. Rudy controls Robot telepathically but has long desired to find a way to be human once again. He needs a new host body for his consciousness, though, which is where Rex Splode becomes involved.
Robot took a sample of Rex Splode's blood so that the young hero can be the basis for his new human form. Robot is unable to clone his original human form without reproducing the same medical issue that put his current body in a containment cell. This leaves Robot with no choice but to find a replacement. He selects Rex Splode in the comics partially due to Monster Girl's attraction to him, and Rudy is interested in a relationship with her, all while helping find a cure for the reversed aging side effect of her transformations. His plan is to transfer the consciousness from his original body to the Rex clone.
The long-term plans of Robot is why he helped the Mauler Twins escape prison at the end of Invincible episode 3. The Maulers have perfected the cloning process and Robot watches the only surviving Mauler in episode 4 to see how he does it. This could mean Robot will try and create a clone of Rex on his own or he can enlist the Mauler Twins' help as he did in the comics. Once Robot sees the second Mauler Twin recreated, phase one of his plan can continue across Invincible season 1.