Hulk villains, actually -- they first appeared in Incredible Hulk #3.
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It's what I thought, Jason, but the thread said they were Spiderfoes. 

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They were often both. These are, after all, not either/or absolutes. As I noted, the Hulk story that introduced the modern version of the Ringmaster and the Circus of Crime was one of the scariest from that era. Indeed, "dark" and "edgy".

In fact, compared to the fare being produced by National/DC Comics, Marvel's product was almost universally "edgier". Consider Spider-Man's origin.

The Masters of Menace or Circus of Crime are one of those neat examples of how things just weren't worked out in advance in those early years at Marvel. In the Ringmaster's first appearance in Hulk # 3 only the Human Cannonball was named. However, in the Ringmaster's second appearance in Amazing # 16 the Human Cannonball was renamed The Great Gambino. He still was the only other Circus of Crime member with a name. When the rest of the team broke away from the Ringmaster and became The Masters of Menace in Amazing # 22 the previously named Gambino went to just Cannonball. Princess Python was introduced and the rest of the team were given names.

This of course is my long winded explaination on why I waited to have them put into the Spider-Foes mix rather than next to the Ringmaster.

I hope to put a real dent into the remaining Ditko vllains next year. On tap for 2013 will be The Spider-Slayer, The Crime Master and The Molten Man.