Prior to Avatar: The Legend of Korra, the only known person to take away someone's bending was Avatar Aang, who took away Firelord Ozai's firebending using energybending. It was presumed this was the only way someone could take away someone's bending, but Amon proved in The Legend of Korra Book One that there was another way to stop someone's bending for good.
Initially, Amon presented himself as a non-bender, and he claimed the spirits gave him the ability to severe a bender's connection to their bending. He would do this by forcing them to kneel and placing his finger on their forehead, and the bender would be unable to bend again. However, Amon's ability was actually linked to bloodbending and chi blocking.
As Book 1 progressed, it was revealed Amon was a Waterbender named Noatak, son of Yakone -- a bloodbending crime boss who started a family in the Northern Water Tribe. He taught Noatak and his other son, Tarrlok, waterbending until they were ready to learn bloodbending. Yakone would then take the brothers on a "hunting" trip, where he revealed his true identity and his ability to bloodbend. From there, the boys learned his ways, with Noatak even mastering Yakone's psychic form of bloodbending.
When Yakone ordered the brothers to use bloodbending against each other, Noatak did so, but Tarrlok could not; however, Noatak came to his brother's defense and bloodbent his father before running away. Between then and the events of Book One, Noatak would become Amon, start the Equalists and learn how to use bloodbending to block someone's bending indefinitely.
While doing this requires bloodbending, Amon's ability also applies a more advanced understanding of chi blocking, which fans were first introduced to with Avatar: The Last Airbender's Ty Lee. As seen with Ty Lee, chi blocking can temporarily inhibit a bender from using their bending, and it can make anyone's muscles useless for a certain amount of time. Anyone can learn chi blocking, and the Equalists have several members who used chi blocking against Korra on multiple occasions.
With how the Equalists and Amon rely on chi blocking for some of their attacks, it's not surprising that Noatak also applied the same logic to bloodbending. Amon created a way to take away a bender's bending by disrupting the chi flowing through their body, and this is likely thanks to his knowledge of chi blocking, as well as his bloodbending. This is so effective that even Katara -- one of the best healers and a waterbender who reluctantly learned bloodbending from the first bloodbender -- could not bring back a bender's bending, despite her being able to treat the effects of Ty Lee's chi blocking before.
Eventually, Korra learned how to undo what Amon did to her and the other benders thanks to her past lives. Aang visited Korra at one of her lowest points, and he touched her forehead like Noatak did, except this time, Aang and their past lives returned Korra's bending and taught her how to do the same for the other benders who fell victim to Amon.
With Korra being the only person known who can undo this, Amon's unique form of bloodbending remains one of the most dangerous abilities in the Avatar franchise. Plus, while Yakone taught both his sons how to bloodbend like him, only Noatak knew how to develop this bending to the point of disrupting another bender's chi.
It is possible another Waterbender could learn to do this, but that would mean they'd have to learn bloodbending, an incredibly rare technique, with Katara being the only living character in the cartoons to know how to use it at this point. They'd also need to learn the logic behind chi blocking. While this technique has become more common thanks to Ty Lee, it's still a unique skill to master. Because of this, Amon's ability to block someone's bending seemingly dies with him.