Sure, Leo was a highly accomplished theologian. After all, it is no accident that he was the first pope to receive the title of "the Great." Leo's Tome was a theological masterpiece that confronted heresy, championed orthodoxy, and insisted upon the fully humanity and divinity of Jesus.Great theologians dedicated their works to Leo out of appreciation for the inspiration that he had been to them. His resistance against heresy brought many who had erred back within the bounds of the Church. This was accomplished by an insistence upon the unity of the Church and a precise argument for what is considered orthodox teaching.
Sure, Leo was a highly accomplished leader. He had been selected to be an emissary of the Church in brokering peace between leaders in Gaul before becoming the pope. While Leo was traveling, the pope died and Leo was selected as the next pope in the intervening time.When he became pope, he was a leader unlike many others by helping to calm and comfort a Rome that was quickly and painfully falling apart. His leadership involved having the power to speak powerfully and truthfully to those who erred in their dogma and doctrine. His letters were received by his audience with a heart nearly as heavy as the one that Leo had in writing them.These letters offered rebuke and called upon the audience to return again to their calling as part of the one Church.
But, when Atilla came to Rome and was preparing to sack and loot it, Leo proceeded out from the city with two assistants and met the mighty warrior on the field of battle. Leo brought a ransom from the vaults of Rome and appealed to Atilla's greed. With the money, Leo also brought an argument against the destruction and violation of the city. He was keen to point out that there were many innocent and uninvolved people in the city that would suffer simply so that Atilla could take home more of the wealth he had already been stripping from the Roman Empire. Atilla was impressed by Leo's demeanor and quiet confidence. Further, he was enticed by the money offered since it came with no risk of life or time. He took Leo's words and money and left Rome.Regrettably, Leo was unsuccessful in negotiating with the Vandals a few years later. They sacked the city but Leo accomplished something else in his negotiations. The Vandals agreed not to burn the city down or murder non-resisting citizens. Though Rome was sacked, its people were offered mercy because of Leo's pleas. Leo died shortly thereafter.