Who is known as Hujjat al-Islam?

Imam Al-Ghazali is known by the title "Hujjat al-Islam" (Proof of Islam). Al-Dhahabi described him in "Siyar A'lam al-Nubala'" (Biographies of Noble Figures) as: "The Shaykh, the Imam, the Ocean, the Proof of Islam, the Wonder of the Age, Zayn al-Din Abu Hamid Muhammad ibn Muhammad ibn Muhammad ibn Ahmad al-Tusi al-Shafi'i al-Ghazali, author of numerous works and possessing extraordinary intelligence."