Splodyhead is an experiment controlled by his fiery disposition: he is fierce, greatly dislikes the water, and is shown to be hotheaded when provoked. He is loyal to his friends, but he does have an attitude. He knows when he's outnumbered, so he will often pick off his victims one by one. He likes his food "well done", as Lilo puts it, which usually means he burns or melts it. While he cannot talk (though he does understand what people are saying), he can still be intelligent and polite, as shown in "Slushy" when he thanked Jumba for fixing him so he wouldn't overheat. He is known to be hostile and apparently shares a grudge with Slushy due to his opposing elemental power, but they resolved it in "Spike".
Experiment 619 was the 619th genetic experiment created by Jumba with Hämsterviel's funding. He was designed to use his fiery plasma blasts to cause massive chaos and damage. 619 and the other first 624 experiments were deactivated and smuggled to Earth by Jumba during his mission to capture Experiment 626.
All of the experiment pods were released and scattered across the island of Kauai.
619's pod was eventually discovered by Lilo, Stitch and Gantu, who were all causing an outdoor ruckus while chasing after it. During their struggle, a seagull snatched the pod and took it back to its nest on a cliff face near the Forbidden Island of Niʻihau. When the gull was unable to peck 619's pod open, it kicked it out of the nest in anger. The pod landed in the ocean, activating 619, who jumped ashore and then proceeded to take over the seagull's nest.
Later, 619 spotted Lilo, Stitch, Jumba, Pleakley, Experiment 625 and Gantu arriving on the island for him. Becoming extremely hostile, he attacked and destroyed both factions' campsites, which put the six in jeopardy. Stitch and Gantu, believing the other one was at fault, had a short-lived battle with each other before Lilo stepped in to break it up.
When the two factions saw 619, whom Lilo named Splodyhead, invading the nest, he attacked with raining plasma blasts, forcing Lilo, Stitch, Jumba, Pleakley, Reuben and Gantu to take cover. Using his plasma attacks, Splodyhead managed to keep the six trapped, yet refused to come down to finish them off, due to him being outnumbered. He then waited quietly to pick them off one by one.
Meanwhile, Stitch and Gantu resumed their conflict, since they both thought the other one was evil. Lilo then told the two rivals that if they wanted to be rescued, they would have to put their differences aside and try to work together. Stitch and Gantu initially refused, but after both factions took a vote, Lilo was nominated to lead them and plan out Splodyhead's capture.
As more time elapsed, the six built and sent out a decoy raft as bait, which Splodyhead targeted and blew up. Convinced the danger was over, Splodyhead left the nest, thus allowing Lilo and Jumba to ambush him and temporarily incapacitate his weapons with water. Defenseless, Splodyhead attempted to escape back to the nest, but was stopped when Stitch tackled him, enabling Gantu to capture Splodyhead in a makeshift net and put him into a containment orb.
Realizing they had worked together, Stitch attempted to make amends with Gantu by shaking hands with the latter, but Gantu ungratefully pushed the former aside. The two factions and Splodyhead were soon rescued from the island by Nani and David driving motorboats, but not before Lilo briefly lectured Gantu's brash nature.
Splodyhead was shortly after taken back to Kauai, where Lilo and Stitch found him a one true place lighting tiki torches at the luau. He also charred a piece of cake with his fiery plasma before devouring it.
In "Houdini", Splodyhead was one of the audience members for Stitch's bungled magic act.
In "Slushy", Jumba adjusted Splodyhead's thermostat so he wouldn't overheat in hot temperatures, to which he politely thanked Jumba in return. Splodyhead was later sent to Slushy's ice palace to defeat the latter. After a long, drawn-out battle between the two experiments, Splodyhead was defeated when Slushy froze him into a block of ice. He was later freed and blasted a fireball into the sky at the top of Waialeale Peak to clear Slushy's snowstorms.
Splodyhead reappeared in "Slugger" as part of Lilo's softball team.
In "Spike", Splodyhead was one of the experiments in Pleakley's E.A.R.W.A.X. group. When a stray snowball from Slushy accidentally hit Splodyhead, who had suffered from boredom, a battle ensued between the two experiments, which ended when Pleakley convinced Slushy and Splodyhead to attempt hugging therapy on each other.
Later, the first 624 experiments, including Splodyhead, were rounded up by Leroy and taken to a stadium to be destroyed. However, Lilo, Stitch, Jumba, Pleakley, Reuben and Gantu arrived before the experiments could be destroyed.
Splodyhead participated in the following battle between the experiments and the Leroy clones by blasting Leroys away with plasma attacks.
However, the Leroys soon gained the upper hand in the battle, but were defeated when Lilo, Stitch, Reuben and several other experiments performed the song "Aloha ʻOe", which caused the Leroy army to shut down due to the original Leroy's fail-safe.
Splodyhead has appeared three times in the Stitch! anime, twice with Plasmoid. In the first appearance, he and Plasmoid fought against Stitch when he was hypnotized by Swirly into fighting for Hämsterviel. In the second appearance, he and Plasmoid were modified by Hämsterviel to attack Stitch. Splodyhead was given a modified ability to fire purple balls of a repulsive odor. Also, after the effects of Hämsterviel were reversed, Splodyhead was able to expel a pleasant aroma, the opposite of his modified ability. He made a third appearance in aiding Stitch in battle against Dark End.
- Splodyhead's arrow-shaped mark on his forehead is similar to that of Aang from Avatar: The Last Airbender.
- Splodyhead's pod color is blue.
- Splodyhead is described by the experiment computer screen as, "Experiment 619. Primary function: Plasma fire shooter."
- In "Slushy", Jumba erroneously refers to Splodyhead as 515, a number taken by Deforestator.
- Splodyhead's head appears in the online game Jumba's Lab.
- Splodyhead made a cameo in Big Hero 6 as one of the pillows on Fred's bed. This makes him the only experiment other than Stitch to appear in a Disney Animated Canon film.