Scepticism or Skepticism - Pyrrho (c.360 - 270 BC)

In the broadest sense of the word  Skepticism or scepticism (see spelling differences) is generally any questioning attitude towards unempirical knowledge or opinions/beliefs stated as facts, or doubt regarding claims that are taken for granted elsewhere. Skepticism is often separated into categories, related to morality (right or wrong), religion (religious doubt), or the nature of knowledge ("there is no knowledge beyond how things appear.")
Xenophanes had taught that we can learn more than know and we can never be sure that we have reached any final truth. Socrates said that the only thing he knew was that he did not know anything. While Xenophanes believed that we could lesson the degree of our ignorance. But both of them took positive attitude towards enquiry and the possibility of learning. 
The first person to make scepticism /skepticism the be-all and end-all of his thought - to adopt it in itself a philosophy , so to speak , and one consisting of an active refusal to believe anything - Pyrrho (c. 365 - 270 BC)
Pyrrho ( c. 360 BC – c. 270 BC), a Greek philosopher ofClassical Antiquity, was a student of Eastern philosophy and is credited as being the first Greek skeptic philosopher and the inspiration for the school known as Pyrrhonism, founded by Aenesidemus in the 1st century BC. He was exposed to Eastern (Indian) philosophy and introduced it to Greece and is popularly known for his skeptic philosophy modeled on the pioneering Indian skeptical philosophical schools and traditions.

Pyrrho was from Elis, on the Ionian Sea. Diogenes Laertius, quoting from Apollodorus of Athens, says that Pyrrho was at first a painter, and that pictures by him were exhibited in the gymnasium at Elis. Later he was diverted to philosophy by the works of Democritus, and according to Diogenes Laertius became acquainted with the Megarian dialectic throughBryson, pupil of Stilpo.

Pyrrho, along with Anaxarchus, travelled with Alexander the Great on his exploration of the East, and studied under the Gymnosophists inIndia and the Magi in Persia. This exposure to Eastern philosophy seems to have inspired him to adopt a life of solitude; returning to Elis, he lived in poor circumstances, but was highly honored by the Elians and also by the Athenians, who conferred upon him the rights of citizenship.

Pyrrho wrote nothing. His doctrines were recorded in the writings of his pupil Timon of Phlius. Unfortunately these works are mostly lost. Today Pyrrho's ideas are known mainly through the book Outlines of Pyrrhonism written by the Greek physician Sextus Empiricus.