The Serpent Society is a group of snake themed supervillains.
They were in the Big House until the Breakout happened. After that, they remained hidden from S.H.I.E.L.D.
They later resurfaced when they took few civilians hostage in an underground railway which got the Avengers' attention to fight them.
Before the fighting, King Cobra had claimed to the Avengers that Madame Viper had sent them a message of support. It actually was Ultron's ruse to distract the Avengers while upgrading his programming.
When the fighting broke out, the Avengers nearly had them until Hank got in their way, trying to negotiate with them and end this peacefully which it failed. Hank's pacifist actions had let the Serpent Society to escape.
First version of the team outside the comics.