He first appears in 'Hypnotrounced', where his dark secrets with Kaa, Savio, Lola, and Viper are revealed.
Hypnorattle's real name is Stephen Rattleback. He was born in Pastoon. He lived with a wonderful and happy family. But then one day, his parents were killed by a rattlesnake-hating gunslinger named the Extinctioner who killed rattlesnakes for the death of his family. As much as Stephen wanted to kill him for this, his venom glands were not matured enough for the venom to be powerful enough to kill, so he was apparently defenseless. But before the Extinctioner could kill him, the local sheriff shot him down. After the Extinctioner's execution, the sheriff took Stephen to an orphanage off world to the Spongebob world, particularly it's own verson of Texas.
After a year in the orphanage, like Tigress, he was considered a monster even though his venom glands were still not matured enough. But although Stephen was feared, he wasn't exactly feared by the people outside the orphanage. One day, Kaa, in his early years, came in the orphanage crying. He wanted a new child to care for after his other 2 children, Lola and Savio, were lost during a monsoon. He chose Stephen, and he became his new father. Kaa desided to take up residence in Nicktoons Texas because he became too depress to go back to Deep Jungle of the India side.
Like every child, Stephen went to school. And like every child, they end up making crap impressions. Stephen and Sandy were rivals since kindergarten (He was stil in toddler years at that time). They even began their first fight in the cafeteria during a fight for the last cactus fruit. After the principal broke up the fight, Stephen swore that he would someday kill her for good. At first, it wasn't taken seriously cause kids have been known to say harsh things when they're upset. However, little did anyone realise, somethings from a child's mouth are not nessersarly born from just being under a hissy fit (snake-based pun unintended), espeically when a heinious tragity cemented that promise into his mindset, implying a possable hatred for mammels because of the Extincutioner.
When Stephen finally matured, and his venom glands finally becoming deadly, Stephen wanted to go kill Sandy like he said, only to discover that she was gone. He learned that when Sandy became 12, she moved into life under the sea to study underwater life, and become a famous inventor. With Sandy gone, Stephen decided to become a hypnotist so he could make a living. Kaa taught Stephen how to hypnotize people with his rattle. It didn't take long before Stephen became a well-paid hypnotist and psychic. He used his skills to help people out of their problems, and even have a bit of fun proving spectics wrong and make them look foolish at the same time. He was even on the verge of dropping his hatred to Sandy for good... But soon, something would ruin that.
However, as we know, power corrupts. Stephen, after being harshly criticsized by a tabliod magizene that, even though no body took it seriously, it broke him emotionally that someone, as uncreditable as they may be, is besmitching his good name just to make a good buck from sells. It worsen it when it turned out to be a rotten cousin of Sandy, Tommy Cheeks, who had wrote that issue of the "Texas Scandelers" that basturdised Stephen as a fraud and swindleing con artist. Dispite the tabliod publishing company having NO credability whatsoever, Stephen ended up getting even with the Tabliod journalists by hypnotising them into making them talk trash about the Mayor and expose his most embarrising secrets, even the one where he's a closet Care Bears fan. It worked both ways. It ironicly made the tabliod more popular cause it had something it didn't had before: proven honest facts. However, the intended effect needed the irony to work. The Mayor natrolly didn't appresiated what the tabliod group did at all, and had it shut down and had every member of it's staff out of work. Stephen felt that it should send a message to the Tabliod industry to never make him look like a fool ever again. However, as careful as he was, even when he kept his exposure anomamus, the cheeks family had their suspitions cause of the fact the publishing company was shot down for all to convinent reasons when an earlier issue mocked Stephen. Based on a hunch, they sued Hypnorattle and with help from a damn good lawyer, exposed that Hypnorattle was respondsable for what happened to the tabliod publsih company. His reputation was destroyed and he was no longer welcomed in Dallas. Kaa was forced to move him to China under the care of the Jade Palace, due to his niece Viper being a member of the furious five. But Hypnorattle became more troubled then he was already, with a revitalised and stronger hatred for Sandy then ever. He then became greedy with his powers that he started controlling everyone around him to do as he said. Even Master Oogway and Master Shifu were vulnerable to Stephen's hypnotic power. That was when Stephen became Hypnorattle. However, Kaa challenged Hypnorattle, and defeated him, cutting off his rattle to prevent him from hypnotizing anyone else. After his defeat, Hypnorattle was sent to prison for his crimes. Because of this, Kaa became depressed again, and went to return back to his native home out of sorrow.
But Hypnorattle's defeat was witnessed by none other than Emperor Fang. Hypnorattle's rattle was retrieved by him, and he broke Hypnorattle out of prison and reattached his rattle. Then Fang offered Hypnorattle to join his Empire, but Hypnorattle refused, and escaped. Then Hypnorattle returned to Pastoon, briefly became a hypnotist again and was grateful to be treated much more warmly then in Texas. However, his hatred for Sandy stayed strong, so did the redesire to rekindle with Kaa, and to do so, he would end up doing it by becoming the greatest and richest criminal in the united universes via stealing the most valuable and powerful stuff in the united universes and sell them off to who ever is welling to pay for it. He made a hide-out out of an old abandoned building into the underground and eventally met Petey, a fly with a troubled history of his own. Stephen's self-absorbed ambitions and his true desires to redeem himself to Kaa and get back his father through a well meaning, but still dark way through still becoming the richest and most successful inter-universeal criminal in history, however, would lead Karma and the Universe to have different plans in mind for his quest to get Kaa back.