In his first model, S.H.E.L.L.D.O.N. was a grey rectangular head with large glowing orange eyes with rectangular horizontal pupils placed on the sides of his head and a yellow grin that glowed brighter when speaking. He has been described as a "hawk bird drone", suggesting an avian-like appearance (though according to Donatello he is neither a bird nor a hawk drone, so this resemblance is not intentional).
In his current model, S.H.E.L.L.D.O.N. has a purple triangular head and a rectangular body with two pairs of rotors that glow light purple on their undersides. He has two pairs of purple ridges on his back (reminiscent of Donnie's flight shell) that are aligned in a 'T' shape, five horizontal grooves on the underside of his body, and a tail. He has large glowing red eyes placed on the sides of his head and his rectangular pupils can be horizontal or vertical. He also has a red line on his face for a mouth that glows brighter when speaking.
When combined with Donnie's battle shell, S.H.E.L.L.D.O.N. appears as a bipedal turtle robot, the shell and his head being the only identical features to his prior form. His glowing purple accents are now located on a dark purple plastron as three lines parallel to each other on his stomach. He has three fingers on each hand and two toes on each foot.
S.H.E.L.L.D.O.N. is initially well-mannered and attentive, much like a butler. Although he is programmed to prioritize Donnie's needs, he still takes the time to serve Raph, Leo, Mikey, and Splinter.
Once the other Turtles reprogram S.H.E.L.L.D.O.N. in "Smart Lair", he adopts a "party dude" attitude and is much more disrespectful to Splinter and especially Donnie, to the point he attempts to kill him in order to replace him as the Turtles' brother. He is later rebuilt to not favor anyone, but his laid-back yet helpful demeanor remains a part of him throughout the rest of his appearances.
Upon S.H.E.L.L.D.O.N.'s version 13 update to his operating system in "Breaking Purple", he behaves much like a defiant teenager, rebellious and sarcastic. He also has a interest in drone racing, so much so that he was grounded by Donnie for racing inside the lair.
S.H.E.L.L.D.O.N. debuted in "Smart Lair". His first model was created to clean the lair for the Turtles to allow them to watch Lou Jitsu Meets the Mummy Ninjas. Initially, Leo, Mikey, and Raph felt warmly toward S.H.E.L.L.D.O.N., until they discovered that he was programmed to prioritize Donnie's needs over theirs. Because of this, the three Turtles rewired S.H.E.L.L.D.O.N. to favor them over Donnie, but he malfunctioned to the point of trying to kill Donnie and replace him as their brother. S.H.E.L.L.D.O.N. eventually captured Donnie with the intention of cutting him with a circular saw, but he was stopped and destroyed by Raph.
Donnie eventually constructed a new model of S.H.E.L.L.D.O.N. and he helped Donnie break into the computer lab of April O'Neil's high school after its active hours in "Mind Meld" on a mission to steal the Dragon's Tooth from the Purple Dragons before they could exploit its immense power. He later assisted Donnie in his plan to trick his brothers into reentering his Mental Intelligence Reprogramulator.
S.H.E.L.L.D.O.N. was ordered by Donnie to fill his position on the team in "The Purple Game" when Donnie was too preoccupied with playing the Purple Game to join the battle against the Purple Dragons' giant destructive mech. By Raph's request, S.H.E.L.L.D.O.N. paired Raph's phone with the mech, allowing Raph to bring the situation to Donnie's attention.
In "End Game", S.H.E.L.L.D.O.N. was called upon by April to become a member of the B-Team in the effort to save the Turtles from the Foot Clan and Baron Draxum after their capture. However, he was unable to free them in the end as he was caught by one of the traps set at the entrance of the Shredder's shrine.
S.H.E.L.L.D.O.N. was scolded for racing inside the lair in "Breaking Purple" by Donnie after he ruined his sandwich. He was confronted by Donnie once more after damaging his dark matter accelerator in his laboratory, but dismissed his grievances. Consequently, he was grounded by Donnie and saddled with a restraining bolt that restricted his mobility. S.H.E.L.L.D.O.N. secretly left the lair later that night and encountered the Purple Dragons on a New York playground. They freed him from his restraining bolt and he accepted their invitation to hang out with them. After becoming a Purple Dragon, he enrolled in that night's drone race for them. However, S.H.E.L.L.D.O.N. was surprised to find Donnie was also competing in the drone race and refused to heed his warnings about the Purple Dragons. Once S.H.E.L.L.D.O.N. lost the race to Donnie, he was swiftly abandoned by the Purple Dragons, much to his dismay. He was then comforted by Donnie and S.H.E.L.L.D.O.N. apologized for the way he treated him.
S.H.E.L.L.D.O.N. gave Hamato Karai tea after Donnie woke her in "Finale Part 2: Shreddy or Not". Upon the Foot's siege on the lair to kill Karai, he was told by Leo to guard her from the Shredder if he found her hiding place inside Donnie's laboratory and then he used one of Donnie's battle shells to transform into an advanced form. However, S.H.E.L.L.D.O.N. was easily destroyed by the Shredder when he eventually invaded the laboratory. It is unknown if he was repaired afterwards or was beyond repair.
- Technology manipulation: S.H.E.L.L.D.O.N. has wireless control over Donnie's other inventions such as his battle shells, laser vacuums, and hovering microwave.
- Multiple limbs: S.H.E.L.L.D.O.N. has many retractable arms. Some have grabbers, much like Donnie's spider shell arms, while others have pointers, sharp daggers, flamethrowers, projectile weapons, drills, sharp spikes, and other various types of weapons and tools.
- Flight: As a drone, S.H.E.L.L.D.O.N. is designed to be able to hover and move around in the air. In his revamped form, he is capable of flying at high speeds.
- Hacking: S.H.E.L.L.D.O.N. is able to hack into machines, such as ATMs, by connecting USB cords from his own body into other computers.
- S.H.E.L.L.D.O.N.'s parent(s)
- Donatello: S.H.E.L.L.D.O.N was created by Donnie and eventually grew to have a father-son relationship with him. In his first incarnation, S.H.E.L.L.D.O.N. gave him frequent compliments and defended him against others' accusations, generally seeking to bolster Donnie's image whenever possible. He used to refer to Donnie as "Master Donatello". After he was reprogrammed, S.H.E.L.L.D.O.N.'s treatment of him changed and he became derisive towards Donnie and carried out his favors with dread. He disliked him to the point he wanted to take his place in the family by killing him. While S.H.E.L.L.D.O.N. no longer harbors such malice towards Donnie, he remains flippant and blunt towards him, though he now listens to him with less reluctance as shown in "Mind Meld". S.H.E.L.L.D.O.N. seems to know Donnie well as he is shown to know how to fool him in "Breaking Purple". He often feels repressed by Donnie and unheard in their relationship. However, after the events of "Breaking Purple", S.H.E.L.L.D.O.N.'s relationship with Donnie has become more positive as they made the effort to see eye to eye.
Friends and Allies
- Raphael: S.H.E.L.L.D.O.N. likes Raph and gets along well with him.
- Michelangelo: S.H.E.L.L.D.O.N. likes Mikey and garnered his sympathy in "Breaking Purple", though Mikey was unable to fully influence Donnie to be more sympathetic towards him.
- Leonardo: S.H.E.L.L.D.O.N. likes Leo and gets along well with him.
- April O'Neil: S.H.E.L.L.D.O.N. was summoned by April in "End Game" to help her and Splinter rescue the Turtles from their captivity.
- Hamato Yoshi / Lou Jitsu / Splinter: S.H.E.L.L.D.O.N. was initially polite towards Splinter, but became brusque towards him after his reprogramming.
- Hamato Karai: S.H.E.L.L.D.O.N. died trying to protect Karai from the Shredder in "Shreddy or Not".
- The Purple Dragons: S.H.E.L.L.D.O.N. joined the Purple Dragons in "Breaking Purple" after he ran away from the lair, allured by their lack of rules and cool demeanors. However, he came to realize that his friendship with the Purple Dragons wasn't real as they merely wanted to use him to possess the Shadow Transmitter and he was abandoned by them.
- Kendra: S.H.E.L.L.D.O.N. was confronted by Kendra when he met her at a playground and she freed him from his restraining bolt, causing him to think that she was benevolent and he accepted her offer of friendship. S.H.E.L.L.D.O.N. was subject to Kendra's insults after he lost the drone race and was deeply hurt by her betrayal.
- Oroku Saki / The Shredder: S.H.E.L.L.D.O.N. rose to defend Karai against the Shredder when she became the target of his violence in "Shreddy or Not", but was defeated by him in the end.
- "Time to snip a branch off the family tree." ("Smart Lair")
- "Brohounds, gotta get out of here! Follow my honest face to safety!" ("Mind Meld")
- "You guys have a giant skate ramp in the house and I can't race?" ("Breaking Purple")
- S.H.E.L.L.D.O.N.'s voice actor, Greg Cipes, also voiced Michelangelo in the 2012 TV series.
- As a nod to this, S.H.E.L.L.D.O.N. occasionally says "Booyakasha!".
- According to Donatello in "Cloak and Swaggart", S.H.E.L.L.D.O.N. has nine ears, all located in various areas of his design, and likes it when others scratch behind said ears.
- Donnie also stated that S.H.E.L.L.D.O.N. requires a change of coolant three times a day.
- S.H.E.L.L.D.O.N.'s first animated appearance actually predated his own in the series, albeit as a CGI model in a 360° promotional video on the Nickelodeon YouTube channel. In this video he went on a "milk rampage" when his "milk feed protocol" was set off by one of the Turtles drinking all of the milk and putting the empty carton back in the fridge, upsetting Donnie greatly.
- S.H.E.L.L.D.O.N. can speak in binary code as shown in "Breaking Purple" and occasionally speaks it to Donnie as Donnie can understand it.