Fifty-one years and counting of Doctor Who has, naturally, resulted in a plethora of different portrayals of its constantly-regenerating protagonist. Not only are there the main incarnations, started by William Hartnell and finishing, for now, with Peter Capaldi, but the one-off and in-between versions, including the ghostly Watcher from the Fourth Doctor's finale; Logopolis, and John Hurt's war torn Doctor from the fiftieth anniversary special. Two of these in-between incarnations, however, I can't help but feel an alarming connection between; the villainous Valeyard and the, uh...Meta-Crisis Doctor.
Before I get into the connection between the two characters, some quick history for any unfamiliar with one or both of them. (This would be a good time for a spoiler alert.) The Valeyard, played by Michael Jayston, was the main antagonist of the season-long Sixth Doctor story; The Trial of a Time Lord. The fourteen-parter saw the Valeyard appearing to be prosecuting the Doctor for tampering with history, when in reality, he was working with the Time Lords to cover up their inadvertently killing the vast majority of the human race by moving the Earth through space. (Why did Clara want the Doctor to save these guys, again?) In return, the Time Lords offered him the Doctor's remaining regenerations, which was good news for the Valeyard, as he wanted to be free of his past self's influence. Yes, the Valeyard, as described by the Master, exists between the Doctor's twelfth and final incarnations. Other media, namely Big Finish's audio plays, have suggested that the Valeyard was the result of the Doctor searching for a way to bypass the thirteen regeneration limit. By the end of Trial, the Valeyard is still out there, so he could very well return in a future season and, being a Time Lord, would not need to be reprised by Michael Jayston.
Now onto the Tenth Doctor--Oops, I mean the Meta-Crisis Doctor. (Sorry, I get them mixed up.) Following the completely natural and necessary cliffhanger in The Stolen Earth, which saw the Tenth Doctor about to regenerate in front of his companions, the conclusion; Journey's End, saw the regeneration conveniently cancelled when the Doctor channeled a portion of the regeneration energy into his severed hand. Consequently, the Doctor doesn't have to change his face this time. (Yay?) But that's not all; later on, Donna touches the hand, which absorbs her human DNA and combines it with its own Time Lord DNA and the absorbed regeneration energy, causing the hand to grow into...This...
And thus the Meta-Crisis Doctor was born. Ultimately, though, he really doesn't do anything practical for the story. His entirely personality and performance is basically copy-pasted from the Tenth Doctor, just slightly less irritating. He doesn't even have much of a symbolic or thematic purpose in the storytelling of the episode. All he does is conveniently kill Davros and the Daleks when the Tenth Doctor's too much of a self-righteous prick to do so himself, and stay in the alternate dimension with Rose so all the fangirls can have their fanfiction. Those are literally the only reasons why he exists; to serve as a deus ex machina to two story arcs, one of which was really already resolved at the end of series 2, but Davies decided to dig it back up because he's Davies. Oh, and Meta-Crisis' mere existence was helpful to Moffat years later, too. In all realism, The Time of the Doctor should not have been the "Final Doctor" story, which should've been reserved for Capaldi's eventual regeneration. However, it's easier for Moffat to write Time if the Doctor has no regenerations then, and the half-regeneration that created Meta-Crisis knocks off the one extra life the Doctor would've had. Thus, Davies essentially allowed his successor a great, big cheat code without even realizing it!
To reiterate, the Meta-Crisis Doctor is not as much a character as he is cheap fanservice for Rose fans and a walking deus ex machina for Davies and Moffat. He has no real purpose outside of simply existing for the convenience of some select people in the real world. But he has the potential to be more. He could have a personality distinct from the Doctor which he is a clone of. The Meta-Crisis Doctor could very well be the Valeyard. If he was, he would cease to be merely a repeated performance from David Tennant and an unnecessary plot device, and would become the Doctor's ultimate foe.
Becoming the Valeyard, of course, won't be as simple as a costume change. Meta-Crisis would have to make his way from the alternate world and into a respected position as a Gallifreyan prosecutor in the past. More importantly, though, why would he even want to leave the parallel Earth in the first place? He seems perfectly content to live a life with Rose. Well, suppose some enemy attacked the parallel world, and Meta-Crisis' efforts weren't enough to save her. In his grief, the cloned Doctor may come to believe his counterpart's influence on Rose's life led her to the circumstances that resulted in her death. Were he to eliminate the Doctor in the past, before meeting Rose, then she very well may still be alive.
But how would Meta-Crisis leave the alternate Earth to enact his plan? Surely, if there's technology that enables time travel and dimension-hopping in the Doctor's universe, there's bound to be some in Meta-Crisis' world, as well. Heck, he may just have to pop down to alternate-UNIT or alternate-Torchwood and borrow some off of a parallel Captain Jack or Brigadier Lethbridge-Stewart (who hopefully won't be wearing an eyepatch in this world. Pertwee fans will get that one.) After getting into the past in the Doctor's world, all Meta-Crisis would have to do is get to Gallifrey. Perhaps he would bump into a classic version of the Master, and explain to him his wish to eliminate the Doctor, convincing the Master to take him to Gallifrey.
Hang on, though; how to explain the difference in actors? The Valeyard can regenerate, but Meta-Crisis, being part human, cannot. This is resolved more easily than some of you may think; all anyone has to do to become a Time Lord is pass at the Academy. (I'm serious, go look it up, or watch Listen and, uh, listen for it.) After that, they expose you to the Time Vortex (hoping you don't get Time Cancer or anything like that.), and voila, you can regenerate twelve times! Meta-Crisis could easily do all this, having the Doctor's memories, including his years at the academy. From there, he could build up a reputation as a prosecutor, and maybe get shot or stabbed along the way and regenerate into Michael Jayston. From there, the Time Lords would offer Meta-Crisis, or as he's called now, the Valeyard, the Sixth Doctor's remaining regenerations in exchange for his help in their big cover-up.
The possibilities on where the Valeyard could go after that are endless! But more importantly than revealing the origins of one of [Doctor Who](series:200668)'s most mysterious villains, having the Meta-Crisis become the Valeyard would also create a true purpose for one of the show's most pointless plot devices. You can't deny that the irony of that situation alone would be intriguing. With the return of Gallifrey possibly on the horizon in series 9 or further on, now could be the ideal time for Meta-Crisis/the Valeyard to return and confront the Doctor once more.