"Beware, my friend. Sankekur may be the most powerful mortal in the world. He controls thousands of fanatical worshippers and embodies the Lord of Hatred, himself. His death will be no easy task."— Natalya(src)
Sankekur was originally a Zakarum priest.
After the death of Que-Hegan Khalim, Sankekur was chosen as his successor as head of the now corrupted Zakarum faith. He was soon after chosen to be Mephisto's host within Sanctuary. At some point during his reign, Sankekur also fell under the will of Mephisto. When Baal and Diablo arrived in Travincal, they quickly freed Mephisto from his soulstone. The Lord of Hatred quickly took possession of Sankekur's body, said body twisting and distorting to mirror Mephisto's form. However, Mephisto was defeated by a group of heroes, and Sankekur presumably slain as a result.
Sankekur's corruption (and indeed, that of the Zakarum faith as a whole) later became public knowledge. It was a revelation that nearly destroyed the organization. Sankekur was succeeded by Que-Hegan Dirae, and the faith took steps to mend its reputation.