What is a Siddha?

In Western literature, a Siddha refers to "one who is accomplished".

In ancient times, the Siddhas emerged from the Kapalikas, who were ascetic Pashupatas during the sixth century. In the following, this text refers to the Siddhas (and Kapalikas) in various traditions of Maha Matsyendra Nath. Today, not much of the authentic Siddha (and Kapalika) traditions is available outside Kaulantak Peeth. But why is that?

The history of the Siddhas

Even though Mahasiddha Ishaputra is referred to as Kaulantak Nath, there is no direct association with the Nath Siddhas. There are commonalities, but there are also differences. In the basic part of this Wiki book, a side by side comparison is out of scope.

"Tantra" describes the ethos of Indian culture of this time; the men who embodied that ethos and the aims and ideals of the culture, the generators and directors of the creative energy that converted the people and transformed society, the guides and exemplars on the path of Tantra, these men were called Siddhas.

Source: Keith Dowman