Pied Piper

The Pied Piper was an energy entity originally from the Jeggorabax Cluster, a region known to house beings feeding on emotions. The Pied Piper manifested a need for fear in order to break loose from a piece of rock it was bound to, known as the Weserbergland Meteorite.

Biography
The entity crashed to Earth in the Weserbergland Mountains in Lower Saxony in 1283, and by the following year had broken loose from the meteorite by feeding on the local inhabitants' fear of the plague. Its first major act was to take the children from the city of Hamelin in order to elicit fear from their parents; an act that made it known as the Pied Piper. (SJA: The Day of the Clown)

The Pied Piper took the children to its own realm, which included such wonders as toffee apple trees and lemonade fountains, but they soon tired of these and began longing for their parents. The Doctor, John and Gillian arrived and decided to help free the children. They travelled to the Pied Piper's castle, who challenged the Doctor to pass three tests or become his prisoner. The Doctor used various technological tricks to pass the tests, then led the children back to Hamelin. (TVC: Challenge of the Piper)

Over the next seven hundred years, he continued to abduct children in order to create fear. One notable stint was an eight year period between 1932 and 1940, in America, as "Odd Bob the Clown". He was also responsible for instilling coulrophobia in young Sarah Jane Smith.

In 2009, he set up Spellman's Magical Museum of the Circus in London in order to steal children from the city. This was made possible by the fact that the Weserbergland Meteorite was on loan to the nearby Pharos Institute. The now adult Sarah Jane Smith prevented him from stealing the children, but he abducted Luke Smith and imprisoned him in his hall of mirrors. With the help of Rani Chandra and Clyde Langer, Sarah Jane overcame her fears, which weakened him to the point where she could force him back into a fragment of the Weserbergland Meteorite. She then placed the fragment in an alien box from which nothing could escape. (SJA: The Day of the Clown)

Alien powers
The Pied Piper was a very powerful entity. Its powers included teleportation, telekinesis, telepathy, shape shifting, limited reality-warping and mind control, although the victim needed to touch or be holding something for him to channel it into them. The entity needed fear to power his abilities.

His shape shifting was the most used of his powers. The Pied Piper transformed his body, clothes and voice to new forms, however, he only showed three forms in total but hinted he could have more.

Behind the scenes

 * Odd Bob seems to have some similarities to Pennywise the Clown in Stephen King's 'It'. Both kidnap children, they both claim to own a fantastical circus, and they look similar. They also share the same name: Pennywise calls himself "Robert Gray" and the Piper's name is Odd Bob, Bob being short for Robert.
 * The Pied Piper's persona of Elijah Spellman resembles the Ghostmaker. From TW: From Out of the Rain.