Abu Issa Mohammed ibn Harun al-Warraq was a 9th Century skeptical scholar and critic of Islam.
He was a mentor and friend of scholar Ibn al-Rawandi in whose work The Book of the Emerald he appears.
Some Muslim sources have described him as being a Muslim and others a Manichaean

Al-Warraq was skeptical of the existence of Allah because "He who orders his slave to do things that he knows him to be incapable of doing, then punishes him, is a fool." Warraq also doubted claims portraying Mohammed as a prophet

That Mohammed could predict certain events does not prove that he was a prophet: he may have been able to guess successfully, but this does not mean that he had real knowledge of the future. And certainly the fact that he was able to recount events from the past does not prove that he was a prophet, because he could have read about those events in the Bible and, if he was illiterate, he could still have had the Bible read to him

Al-Warraq challenged the notion that Islam was a revealed religion. He argued that if humans are capable of figuring out that, for instance, it is good to be forgiving, then a prophet is unnecessary, and that we should not heed the claims of self-appointed prophets if what is claimed is found to be contrary to good sense and reason

Warraq admired the intellect not for its capacity to submit to a god, but rather for its inquisitiveness towards the wonders of science.

He explained that people developed the science of astronomy by gazing at the sky, and that no prophet was necessary to show them how to gaze. He also said that no prophets were needed to show them how to make flutes, either, or how to play them