Serling is a robot from the year 2105, Serling serves as butler and caretaker to Cody Jones, a role he has held for the entirety of Cody's life, having been more family to him than Darius Dun. Proper and refined (although not without a flair for drama and sarcasm), Serling is quite appalled by the presence of the Ninja Turtles and the chaos they have bought into Cody and his life, although he eventually comes to accept that, like him, they have Cody's best interests at heart.
Although a later model of the robot, the Servatron, that eventually became Turtle X, Serling initially possessed none of its battle ability, making him a rather ineffective protector. Despite this handicap, Serling was unhesitant in risking his "life" to save Cody during his captivity inside a berserk Turtle X, and was as a result heavily damaged. Fortunately, Cody managed to repair him and reconfigure him into a new Turtle X armor, which he can now change into at will.
Serling has been taking care of Cody since he was a baby, having always been there for him, even when he lost his parents.
When Cody created a time window to view the Turtles exploits in the past, he accidentally brought them and Splinter into his time. Serling went out to retrieve them, saving them (excluding Mikey) from the Peacekeepers and giving them filters to breathe in the multi-breathing air. When they find Mikey, Serling gives him the same gear he gave the others.
When it appeared that the Turtles were going to stay until Cody could perfect the time window, Serling had to put up with them, as they made a big mess in the penthouse, smashing an antiques.
When the Turtles are trapped within the new Gaminator program, Cody learns that Serling can touch them without being affected by the neural fields and uses him as a link to download some "cheat codes" to the Turtles. But when they defeat Viral, the Turtles send Serling back in the game
On Cody's birthday, everyone was prepared to keep it a secret. Serling had complied a number of video files of him and Cody but decided to erase the one with Darius. By coincidence, Cody was trapped in his own Turtle X armor being controlled by Dun. In determination to save his master, Serling downloads the anti-virus program into himself and goes after the rogue Turtle X, copying the Turtles' line, "It's ninja time", into "It's Serling time". Having learned much from them, he creates a big mess by ripping off Turtle X's right arm but gets heavily damaged before finishing the download. Cody promises to fix him and remakes him as the new Turtle X armor.
Cody and Serling disobey President Bishop's direct order to not follow him and the Turtles to Moonbase Bishop. They arrive just in time to save them from becoming Kanabo drones. Serling was also ready for Viral, trapping her with a decompiler.
Serling is prim, proper and refined much like most butlers in fiction, Serling has great distaste for things that he doesn't consider appropriate nor does he like the chaos that occurs when the turtles and Splinter are around. He also has a flair for drama and sarcasm. He can also be somewhat supercilious and pompous towards the turtles.
Serling was excited that the Turtles were going to be going home. But unaware to him, Viral had reconstituted herself inside him and took control of him and the time window, landing the Turtles, Splinter and him in the dinosaurs ages. Worse, Viral had disabled all of his defense protocols. After a trip to the Dark Ages and then the not-too distant future with three Shredders, Serling was damaged by an entirely new one. Don was able to repair him with a coil from the Utrom Shredder's exo-suit, rebooting all his systems. Don gets inside Serling's Turtle X mode, using the decompiler on viral and escape back to the present time. But Viral reinfects Serling uses the uses the decompiler on Splinter.
Now in the 21st century, Serling was overjoyed to actually meet April and Casey.
Serling secretly tried to construct a makeshift time window to return to 2105. He acted generous to the Turtles, giving Leo a direction to a Feudal Japan weapons exhibit, Mikey a movie ticket, Raph a ticket to a wrestling match and Don directions of more of Splinter's pieces. Unfortunately, when he activates the window, it accidentally shrinks him to five inches tall and when he kicks it, he is transported to the dinosaur ages, where he is grabbed by a pterodactyl. Another portal whisks him to probably the 1920s, where he blasts a clockwork toy soldier owned by a kid named Wendell. Serling's last portal takes him to the Turtles' toddler ages. To prevent them from knowing he's alive, he activates his inner monologue so that he could speak inside. The Turtles tossed him about like a play toy before Splinter took him away until they learned responsibility. But during the night, Mikey tried to sneak Serling but in a fight with his brothers, accidentally loses him in the streets.
As he makes his getaway, he is knocked off the road by a car that was driven by a much older Wendell, who sees Serling as "cherished", as seeing him blast his toy, wants to find and reproduce him. Just as Wendell is about to cut Serling open, the Turtles, who followed Wendell, save Serling. Angry that they have taken his "cherished", Wendell unleashes a number of incarnations of Serling toys. To help the Turtles for saving his life, Serling controls a number of other toys in the store so that he wouldn't have to reveal his true nature. But splinter, who had also followed them, had to fight a life-sized robot. Serling managed to take out its batteries. The Turtles decide they don't want Serling and give him to Wendell but he decides to let go of his life obsession. Serling then begins to insult them, so they throw him in the trash. He is then transported back to the present by their older selves.
In the events of Turtles Forever, Serling is absent. However it is assumed that he was sent back to the future.