Spencer Smythe was an inventor of the original Spider-Slayer. He managed to convince J. Jonah Jameson to use it in his campaign against Spider-Man. He also worked with Mark Raxton on creating a liquid metallic alloy for the Spider-Slayers, which eventually turned Raxton into the Molten Man. He next constructed the Spider-Slayer Mark II.
As he was dying of radiation poisoning, he wanted to take revenge on J. Jonah Jameson and kidnapped his son John and controlled him to attack the senior Jameson. After this failed and John disappeared, Smythe shackled Jameson and Spider-Man together to a bomb. He set the timer to go off after twenty-four hours because he wanted to see them die, but ultimately he died before this happened. Spider-Man was able to freeze the locking mechanism, allowing the shackle to come loose, which he quickly discarded seconds before it exploded.
When Jameson became Mayor of New York in 2009, he managed to legally acquire Spencer's devices to augment his Spider-Slayer squad to capture Spider-Man, including his spider tracer. However, his squad had a change of heart after Spider-Man helped them to surround a nuclear bomb set by the Chameleon and crushed the tracer.
His son Alistair inherited the Spider-Slayer legacy and gained a new-found hatred toward Spider-Man.