It is unknown why the Italian aerialists the Great Gambonnos joined the Circus of Crime, but they have been long standing members seemingly only missing their first appearance against the Hulk. They consider themselves to be the "Kings of the Trapeze", and they effectively use their acrobatic skills in tandem to cause confusion, but they were unable to best either Spider-Man or Daredevil. 
 
The identical twins joined the Clown, Princess Python, and the Human Cannonball in the Masters of Menace, wanting to break from the Ringmaster and hoping for better success. However, when Spider-Man stopped their criminal endeavors, the returned to Ringmaster and the Circus of Crime.