|“||The only thing keeping us safe right now is the government thinks we died in Atlanta. We have to be careful.||”|
The Mutant Underground is a mutant controlled resistance group operating against the Sentinel Services and their mutant hunting operations. They seek to provide refuge for persecuted mutants, and fight back against the corrupt government designed to imprison them.
The Mutant Underground is a nationwide network that was founded after the anti-mutant laws were enacted. The network was created shortly before the X-Men (their founders) and the Brotherhood of Mutants disappeared.
Initially, their only goal was to provide refuge for persecuted mutants, but when it was discovered that mutants were being forced into hunting each other for Sentinel Services, the Underground made it their secondary objective to put an end to it and all other anti-mutant agendas. This, in turn, brought them into conflict with Hellfire Club, who preferred using extreme measures to achieve their goals. Eventually, some members of the Mutant Underground left to join the Hellfire Club, believing the Underground wouldn't do what was necessary to ensure the survival of mutantkind. Those members include Polaris, Sage, Bulk, Fade, and Andy Strucker.
The remnants of Thunderbird's cell of the Mutant Underground relocated to Washington D.C. in search of their former allies. They then made Potomac Salvage their new HQ. In the aftermath of the destruction of their former headquarters in Atlanta, the government was led to believe they had perished, leading the Underground to continue their operations in secret.
Throughout the SeriesEdit
- The Mutant Underground is inspired by the Underground Railroad. 
- Shortly before they disappeared, the X-Men founded the Mutant Underground in the aftermath of the 7/15 crisis and appointed Thunderbird as one of the leaders.