Aguero signed for Manchester City from Atletico Madrid in 2011 for a reported £38m fee and has become a crucial goalscorer for the North-West outfit.
Benitez, who took charge at Newcastle last month, has revealed that during his six-year spell as Liverpool manager, Aguero could have joined the Merseyside outfit but he ended up signing for Atletico from Independiente in 2006.
"Sergio was helping me," Benitez told reporters. "We have a foundation in Liverpool. Sometimes I am asked for shirts to be signed to make some money and he was one of the nice people.
"I was Liverpool manager, they offered him to us as a young player for big, big money. He signed for Atletico Madrid. He was a player that we knew. We were following him. We knew he was a very good player then."
Newcastle will take on City at St James' Park tonight.