Jamal al-Din al-Afghani was the founder of Islamic revivalism, the movement to restore Muslim civilisation to its former glory. Al-Afghani was an activist who travelled around the Islamic and European worlds preaching political and religious reform, being courted, getting exiled, and generally creating controversy.
Al-Afghani called for pan-Arab unity as a response to western colonialism -- the main voice among many. He claimed Afghan Sunni descent (hence the name al-Afghani), but many believe he was in fact of Persian Shia origin. From 1884 onwards he published from his base in Paris, together with his student Muhammad Abduh, the Firmest Bond, an important anti-imperialist journal protesting against British colonialism in Egypt and Sudan.
Al-Afghani was described as a liberal by English contemporaries, including Wilfrid Scawen Blunt. Towards the end of his life he was a prominent agitator in the run-up to the Iranian constitutional revolution, leading to his eviction from Iran in 1891.
However, there is little proof that he ascribed to European liberalism, and his deference to intellectuals such as Ernest Renan was aimed at defending Islam, rather than adopting European ideas.
On the rationality of Islam:
The Islamic religion is the only religion that censures belief without proof.