Sparky prefers to be left alone, using its powers and combining them with a hot and defensive temper when provoked. He longs to be free, and is otherwise "harmless," his only goal to carry out his primary function.
In Stitch! The Movie, he is the first of the original experiments to be activated (Before activation, all experiments are in pod form, excluding Stitch). He is activated by Lilo and Stitch. However, he goes on a rampage throughout the town, shorting out any electrical appliances in sight. Soon, Lilo and Stitch manage to catch him, and convince him to be good. He helps out in saving Jumba, by shorting out Gantu's ship. Lilo decides that Experiment 221's one true place is at an abandoned lighthouse, where he can make the giant sized light work again, and as it's big enough, he will not short it out when he touches it.
After the film, Sparky became a supporting character in the series. Lilo and Stitch often visited him along with other experiments for various problems. In one episode he and some other experiments were seen in Lilo's dream in a conga line. In another episode Sparky was summoned by Lilo and Stitch to help rescue captive experiments from Gantu's ship including Angel.
In the film Sparky can be seen waving hello to Stitch and Lilo. Later on Sparky is captured by Leroy and taken captive to an arena where he and the other experiments are nearly obliterated until Stitch storms in. A war follows between the experiments and the Leroy clones. Sparky uses his incredible shock waves to defeat the villains. In the end the clones are destroyed and Sparky resumes his job at the lighthouse.
Role in the Spongebob series
In the spongebob series, Sparky reprises his role form the two films above, but his battle against Stitch is also enhanced by the fact that he is accompanied by several of the Dark Dragon's shadow goons, as they are partially possessing him in order to turn him into a Heartless. Thankfully, Sparky is defeated and the Heartless-ification is canceled in time.
Later on, in Leroy and Stitch, Sparky participates in the final boss battle against Hamsterviel's Heartless Army, managing to take down a few Leroy Heartless with his thundershock attacks.