Green Goblin- Spider-Man #75 / Spider-Man: Revelations
In Peter Parker: Spider-Man #75 (Spider-Man: Revelations) the Green Goblin reveals that he is the one responsible for the Clone Saga, which lasted over two years, that is usually attributed to the villain Jackal. The clone saga is one of the most ridiculous, and ridiculously long lasting, stories in comic history- though the first few issues did have some pretty unique ideas. Further information on Green Goblin's involvement in the clone saga can be found in Spider-Man: The Osborn Journal.
Ben Reilly was a prominent figure in the Spider-Man Clone Saga. As a Parker clone, Ben worked beside Spider-Man under the name Scarlet Spider. There is even a moment in the series where test results come back, manipulated by the Green Goblin, claiming Ben to be the "real" Peter Parker. The results cause Peter to question both his mental stability and his life's purpose.