WARNING: The following contains spoilers for Dark Ages #1 & What If...? Episode 4, now available for purchase from Marvel Comics and streaming on Disney+, respectively.
Doctor Strange has always been established as one of Marvel's most potentially powerful figures, capable of changing the entire face of reality with nothing but a forceful command and intricate spell. But if that power is unleashed in the wrong direction, it's very easy for the Sorceror Supreme to become the kind of destructive force he often charges himself with fighting back against.
This was reiterated twice in alternate universes this past week, with the Doctor Strange who appears in Dark Ages #1 by Tom Taylor, Iban Coello, Brian Reber and VC's Joe Sabino and in What If...?'s fourth episode, "What If... Doctor Strange Lost His Heart Instead of His Hands?"
In Dark Ages, the ancient Unmaker -- a being of universal power and capable of absorbing black holes -- was corrupted and brought chaos across the cosmos. The Living Tribunal was able to defeat and contain the force and hid it within the core of a newly formed world -- Earth. When the Unmaker awoke, it caused massive destruction around the globe. Aware that it fully reactivating would result in the end of the world, a small contingent of heroes went to confront the force. As their friends died around them, Invisible Woman's shields collapsed and Doctor Strange was mortally wounded -- but not before opening up a portal to a dimension that's home to a unique EMP blast, stopping the Unmaker. But due to his death, Doctor Strange couldn't close the portal, costing humanity all technology.
Meanwhile, the Doctor Strange of "What If... Doctor Strange Lost His Heart Instead of His Hands?" came from a reality where he was still in a relationship with Christine Palmer on the fateful night of his car crash. Losing the love of his life instead of his hands resulted in a more skilled Doctor Strange -- but one who was willing to break the laws of reality to try and get Christine back. His actions ultimately resulted in the shattering of an Absolute Point -- creating a paradox that ate away at the world and destroyed everything in existence except for a small pocket of reality that contained Strange and the resurrected Christine. But even she faded away, and the Watcher could only tell off Strange for his callous actions that destroyed an entire universe.
Both are a painful reminder of just how strong Doctor Strange can really be. His plan in Dark Ages was at least well thought out and involved saving the entire world -- but the loss of mechanics around the globe quickly resulted in untold destruction and death. Any and all artificial life ceased to function, and any machines keeping people alive failed. But at least he wasn't as bad as his What If...? counterpart, whose reckless actions resulted in the loss of all life across his entire reality. These aren't anomalies either, with Doctor Strange's powers shown capable of surviving the entire destruction of whole planes of existence or recreating the Earth after it was briefly destroyed in Marvel Premiere #13 and #14 by Steve Englehart, Frank Brunner and Dick Giordano.
Doctor Strange is regarded as one of Marvel's most powerful characters for a reason. In a single day across two realities, he irrevocably changed -- or destroyed -- entire incarnations of the Marvel Universe. That should be a good indicator of the kind of power vacuum about to be left open in the upcoming Death of Doctor Strange storyline, which will see the Earth besieged by an entirely new class of mystical threats that the Sorceror Supreme won't be around to contend with.