Shukaku is the one tailed bijuu in the anime Naruto, Naruto Shippuden and later in Boruto. Shukaku is introduced in the 135 manga chapter and episode 78. It was believed that he was the vengeful spirit of an old monk that had been sealed within a tea kettle. Of all of the tailed beast he was the first to have had his name revealed.
The tailed beasts in Naruto are commonly known as Bijuu. The Bijuu are also referred to as "Chakra Monsters", since they are living forms of chakra. The tailed beasts have a history of their own and here it is.