WARNING: The following contains spoilers for The Death of Doctor Strange #1 available now from Marvel Comics.
The first issue of The Death of Doctor Strange (by Jed McKay, Lee Garbett, Antonio Fabela and VC’s Cory Petit) wastes no time getting to the point. Strange starts his day talking with Wong, performing surgery, and teaching at the Strange Academy. He reminisces on an old fable and those he has lost.
After returning to an empty Sanctum Santorum he goes to relax, only to hear a knock at the door. As he opens it, he seems to know who is on the other side, but fails to realize their intentions. He is overpowered, by magic that should not be possible to wield and stabbed in the heart with a dagger. His death is felt around the world, and many powerful mystics arrive at the scene, some friends others foes. Here are some of the potential suspects that could have been responsible for the death of Marvel's Sorcerer Supreme.
Baron Mordo
As one of Strange’s most infamous adversaries, he and his servant Kaecilius arrive shortly after the death of his nemesis. Mordo admits he has always wanted to kill the sorcerer, and is outraged that someone has beaten him to the task.
However, Baron Mordo has proven capable of taking on the Sorcerer Supreme several times in the past, and is one of the few magic users in the world who approach Strange's level of proficiency in the arts. Furthermore, if he is responsible for the death, he would certainly lie to cover up the fact.
Brother Voodoo
While usually considered to be an ally, the former Sorcerer Supreme Jericho Drumm may still be upset by the death of his brother Daniel due to a plan initiated by Strange going south in Savage Avengers #12 (by Gerry Duggan, Adam Gorham and Travis Lanham).
Even though Daniel Drumm was working with the Hand, Elektra didn’t hesitate to kill Daniel right in front of Jericho. Voodoo seemed to accept the loss, but may have understandably harbored ill will toward Strange. Voodoo may also wish to retake the mantle of Sorcerer Supreme that is now left vacant in the wake of the death.
Clea and/or her father
During the issue, Strange looks at a picture of Clea he keeps on his bathroom mirror. While they were married at one point, their relationship became strained after she returned from the Dark Dimension where she ruled. After she helped Strange and the Defenders when they were cursed, the two divorced and she returned to rule her dimension. She is also the niece of Dormammu.
Clea's father, Orini was actually the legitimate heir to the Dark Dimension and continues to be a loyal disciple of Dormammu. It is not beyond the realm of possibility that Orini could have done the deed at the behest of his dark master or because of his daughter's relationship with Strange.
Doctor Doom
Even though Doom showed up to help Strange's Savage Avengers face the sorcerer Kulan Gath, he has most recently been seen in space working with the Guardians of the Galaxy and on Mars with the X-Men. After Dormammu possessed Ego the Living Planet he and the Guardians worked together to defeat him.
Doom may dabble in the mystic arts, but it seems unlikely he could possess the ability to wield magic strong enough to subdue the Sorcerer Supreme. If he did come to the Sanctum Santorum, it is also doubtful that Strange would let his guard down. Still, Doom was initially taught magic by Strange, and the two developed a healthy respect for one another when they ventured to hell to rescue the spirit of Doom's mother. Furthermore, Doom is known for stealing the powers of others when needed, and Strange commented at the time of his death that his assailant should not be able to wield so much power. All of this could point to Doom being the culprit, although his motivations for doing so remain uncertain.
Doctor Strange
The strangest possible suspect of the murder is Strange himself, or at least the version of him that arrives at the end of the issue to "help" his mystical allies find the true culprit.
The much younger doctor reveals that his current day counterpart had a contingency plan in place in the event of his death. However, there is also the possibility that this version of the Sorcerer Supreme has been corrupted as he was previously in the comics by Dormammu, and in the MCU's What If...? when he was overtaken by a thirst for more power.
Doyle Dormammu
Appearing earlier in the issue, Doyle is the son of Dormammu, who is one of Strange’s most powerful adversaries. Although he has been a student of Strange Academy since its inception and he comes to Strange with a warning, it is entirely possible that Doyle is not the ally he appears to be.
In Strange Academy, Doyle Dormammu has had visions of becoming as evil as his father. This could be a manifestation of that, or it could be his father working through him to get Strange to drop his guard. This would explain the Sorcerer Supreme dropping his guard as well as his exclamation that his assailant should not possess the level of power that was used against him.
Magik
Like Doyle, Magik appeared earlier in the issue helping Doctor Strange defeat demons that had escaped out of the Limbo dimension. With a new Inferno on the horizon, she could be giving into her dark urges and be on the brink of transforming into the corrupt Darkchylde.
With her being a member of the faculty of Strange Academy as well as being previously trained by him, there is no doubt that the doctor would let her into his home and drop his guard. She also would be able to wield an uncanny amount of magical power if she has given in to her more powerful persona.
Scarlet Witch
Following the events of the Hellfire Gala, Wanda Maximoff should be dead for all intents purposes. If Wanda showed up alive at his door, it would certainly explain his surprise, as well as his dropping his guard. Her mental instability also means that her control and strength can be unpredictable, resulting in the magic wielded being beyond what was thought possible.
Whoever is responsible for the death knew that without Strange the world would not be protected from invasions from other dimensions. The death also brings to light the equally important question of who will be the new Sorcerer Supreme...and if they are prepared to face the new threat waiting on the horizon.