Which pope called for the Second Crusade in 1145?

The pope who called for the Second Crusade in 1145 was Pope Eugene III.

Eugene III responded to the fall of Edessa, the first major Crusader state, to the Muslim ruler Zengi in 1144. On 1 December 1145, he issued the papal bull Quantum praedecessores, urging King Louis VII of France and other western Christian rulers to take up the cross and launch a new expedition to the Holy Land.

Eugene was a Cistercian monk and the first member of that order to become pope. Because he lacked the political and military reach to lead the campaign personally, he relied heavily on Bernard of Clairvaux, one of the most influential churchmen of the period. Bernard preached the crusade across Europe, helping persuade Louis VII and the German king Conrad III to participate.

The other options were previous or subsequent popes connected to the turbulent papal politics of the era, but they did not issue the call for the Second Crusade. The expedition ultimately suffered a major setback at Damascus in 1148 and failed to recover Edessa.