The Spider-Slayers are a series of robots designed to hunt down and defeat Spider-Man.
Black Widow was designed by Spencer Smythe for Norman Osborn. It accidentally kidnapped Flash Thompson in a Spider-Man costume. Spider-Man rescued him and dropped the Black Widow into a vat of acid. Spencer apparently died so his son Alistair Smythe built Black Widow II, Tarantula, and Scorpion for the Kingpin. The three could combine. He sent them after Flash, Spider-Man, J. Jonah Jameson, Eddie Brock, and Norman Osborn. Spider-Man defeated them with a bomb and they fell into the Hudson River. He later built the more humanoid Mega Slayer. It stole the Tablet of Time and Alisha Silvermane but was defeated. When Kingpin hired Herbert Landon, they turned Alistair into the cyborg Ultimate Slayer. However, Alistair broke through his programming and realized that his father was still alive. Smythe and Mega Slayer were present at the wedding of Peter Parker and Mary Jane Watson. Smythe later participated in the Secret Wars.
Tarantula and Scorpion were not named. Their combined form is only named the Tri-Slayer in toys.
Spencer Smythe lived long enough to design many different Spider-Slayers.
Alistair became the Ultimate Slayer before designing Black Widow, Tarantula, and Scorpion.