Alexander Marcus (alternate reality)
Admiral Alexander Marcus was the head of Starfleet in the mid-23rd century, and a member of Section 31. He began a conspiracy to start a war with the Klingons using the 20th century genetically-enhanced Human criminal . He was the father of .

Early life 
Alexander Marcus was the head of Starfleet. At some point, Marcus had a daughter named Carol with a woman who had the maiden name Wallace. He was also the mentor of  and inspired him to join Starfleet. Having been raised by him, Carol believed (ultimately incorrectly) that her father was incapable of killing innocents. ()

Starfleet career

Revival of Khan

Following the destruction of  in 2258, () Marcus began seeking ways to militarize and better defend the Federation. In particular, he considered war with the Klingon Empire as inevitable. Section 31 discovered the  which led to Marcus reviving Khan Noonien Singh and recruiting him under the name "John Harrison" to design weapons and ships.

However, Khan resented Marcus' control over him and the use of his fellow surviving Augments as hostages, and attempted to smuggle them out in the experimental photon torpedoes he created. He was discovered, and Khan was forced to flee alone, beginning a one-man war on the Federation as he presumed Marcus killed his crew.

Kirk's demotion
When Captain  violated the Prime Directive while on Nibiru, the matter was brought to Marcus' attention who, as punishment, confiscated the  from him and sent him back to Starfleet Academy. However, Pike convinced Marcus to alter the punishment for his protégé. Kirk was instead demoted to Pike's first officer.

Conspiracy

On stardate 2259.55, Khan coerced Section 31 agent Thomas Harewood into bombing the Kelvin Memorial Archive in London. Marcus received a message from Harewood before he died explaining Harrison threatened him, and the admiral declared a manhunt at a summit in Starfleet Headquarters. Khan, aware protocol dictated a summit like this one, appeared in an attack vehicle and opened fire. However, Khan was forced to flee and Marcus survived, though Pike was killed.

The following morning, Kirk reported Harrison had used the confiscated transwarp beaming formula to escape to Qo'noS. Marcus ordered Kirk to pinpoint and execute Khan with the seventy-two experimental photon torpedoes he had designed. 

Once Kirk discovered the truth from Khan, Marcus showed up in the  (a warship designed by Khan), intent on retrieving Khan and destroying the Enterprise and it’s crew to cover up his crimes. Refusing Marcus’s orders to hand Khan over, Kirk attempted to flee to Earth in the hopes of putting Khan on trial and exposing Marcus. However, the Vengeance caught up and crippled the Enterprise in warp space. Marcus' daughter Carol revealed she was on the Enterprise in a bid to get him to spare the ship and its crew, but the admiral simply had her beamed up and proceeded to order his crew to destroy the ship. Fortunately,  had smuggled himself aboard the Vengeance at coordinates given by Khan and deactivated its weapons. Khan and Kirk donned thruster suits and flew over to the ship to commandeer the bridge, during which Khan saved Kirk's life when the display compass in Kirk's helmet went dead leaving Kirk flying blind. Khan found Kirk amid the debris and guided him in.

After taking over the bridge, Kirk, believing that Khan intended to betray them, ordered Scott to stun Khan. Kirk then confronted Marcus over his betrayal of everything the Federation stood for, but Marcus angrily insisted that his actions were justified, and that without him the Federation would be destroyed in what he considered to be an inevitable war with the Klingons, a war he, ironically, was trying to start in the first place. Suddenly, Khan, having only pretended to have been stunned, assaulted Scott, Kirk and Carol. Marcus briefly escaped to a console near the back of the bridge, but before he could achieve anything, Khan caught up with the admiral and began crushing his skull with his bare hands, angrily telling Marcus that he should’ve let him sleep before killing him, whilst prompting a horrified scream from Carol. ()

Legacy 
Immediately after killing him, Khan took control of Marcus's ship and held Kirk, Scott and Carol hostage, demanding that Spock surrender his crew or face destruction. Spock complied, allowing Khan to transport the 72 torpedoes to the Vengeance and transport Kirk Scott and Carol back onto the Enterprise. Spock, having anticipated Khan's betrayal, had ordered Doctor  to remove the cryo tubes from the torpedoes and had them armed within the Vengeances cargo bay. The detonation crippled the ship and led Khan to believe that his crew were killed. 

The battle caused both starships to fall down towards Earth. The Enterprise averted crashing, but Khan directed the Vengeance into downtown San Francisco in an attempt to Starfleet Headquarters in a final act of spite. He attempted to escape, but was apprehended by Spock and . Khan's blood was used to revive Kirk, who had suffered fatal radiation poisoning from saving the Enterprise, and he was placed back in stasis with the rest of his crew.

Nearly a year later, Kirk spoke at a memorial for the lives lost as a result of Admiral Marcus and Khan's actions. In his speech, Kirk reminded the attendees that Starfleet's true mission was not to militarize the Federation, but to explore the galaxy. As the rechristened Enterprise began to embark on the first five-year mission, Kirk expressed gratitude of Carol being part of the "family", to which she stated that it was nice to have a family. () 

By 2263, Marcus's conspiracy ultimately dissolved since, as Montgomery Scott once stated, Starfleet was not a military organization. ()

Memorable quotes
"By now, some of you have heard what happened in London. The target was a Starfleet Data Archive, now it's a damn hole in the ground, forty-two men and women are dead. One hour ago, I received a message from a Starfleet officer who confessed to carrying out this attack, that he was being forced to do it by this man: Commander John Harrison. He's one of our own, and he's the man responsible for this act of savagery. For reasons unknown, John Harrison has just declared a one-man war against Starfleet, and under no circumstances are we to allow this man to escape Federation space. You here tonight represent the senior command of all the vessels in the region, and in the name of those we lost, you will run this bastard down. This is a manhunt, pure and simple, so let's get to work."
- Alexander Marcus, explaining the London bombing.

"Earth's perimeter sensors have not detected any warp signatures leaving the system, so we know he can't be far. You will park your ships in a blockade formation then deploy search vehicles and landing parties to run down every lead. This man has shown willingness to kill innocent people, so the rules of engagement are simple. If you come across this man and fear for your life or the lives of those nearby, you are authorized to use deadly force on sight."
- Alexander Marcus, explaining the hunt for John Harrison

"You got something to say Kirk, say it. Tomorrow's too late."
- Alexander Marcus, to James Kirk about his outburst

"All-out war with the Klingons is inevitable, Mr. Kirk. If you ask me, it's already begun. Since we learned of their existence, the Klingon Empire has conquered and occupied two planets that we know of, fired on our ships half a dozen times. They are coming our way."
 - Alexander Marcus, to James Kirk, about the tensions between the Federation and the Klingons

"Well, shit! You talked to him."
- Alexander Marcus, upon realizing that James Kirk knows John Harrison's true identity

"That's a hell of an apology, son. But if it's any consolation, I was never gonna spare your crew. Fire when…"
- Alexander Marcus, after James Kirk offers himself in return for the Enterprises safety

"You better stop and think about what you're doing, Kirk. You better think about what you did on Qo'noS. You made an incursion onto an enemy planet! You killed a Klingon patrol. Even if you got away without a trace, war is coming. And who's gonna lead us?! YOU?! If I'm not in charge, our entire way of life is decimated! So, you want me off this ship, you better kill me."
- Alexander Marcus, to James Kirk, with the latter trying to arrest him at gunpoint

Appendices
 Background information 
Admiral Marcus was played by Peter Weller, who also played John Frederick Paxton in . The character was described by producers Damon Lindelof and Bryan Burk as being their attempt to incorporate a trope of Hong Kong cinema into the film, in which the hero (Kirk) and villain (Khan) must temporarily set aside their differences. 

Weller compared Marcus to General , the Chief of Staff of the United States Air Force in the 1960s, and a proponent of nuclear war. LeMay "had eighteen nukes stored on his own that he didn't tell the  or President Kennedy about – because he didn't deem them knowledgeable enough about war. That is unbelievable arrogance! So, Admiral Marcus is basically like LeMay."  However, he opined that Marcus actually has a conscience because he wants to undo his mistake, but what "makes him bad, from a moralistic view, is that he's willing to sacrifice Kirk and the Enterprise to put this thing back in its shell."  

Weller also disliked that people thought of Marcus as a "bad guy", stating, "Everything he says is true: the Klingons are coming, they do need Khan, and that's that. It's just that he’s going to sacrifice the entire Enterprise to get the job done, because the Enterprise started to believe Khan. But if the Enterprise had not believed Khan and had done what Marcus said, then there'd be no movie, and everything would be cool. But the great writing in this is that the Enterprise wakes the dude up and listens to his game, and then everything goes to crap. But that's the Enterprises hubris. That's them. They screwed up, not Marcus. Anyway, sorry to go off there. I just hate that." 

Weller added he liked the character's name because it reminded him of Alexander the Great and .   found parallels between Marcus and , to which Simon Pegg responded "Absolutely, he's definitely a Republican." 

 Apocrypha 
The IDW comic series Star Trek: Countdown to Darkness, set in the alternate reality, reveals that Marcus was the first officer of a previous  which existed subsequent to , but prior to the new  and was a friend to Captain . 

In addition, "" indicated that, as a commander, Marcus served on the admissions board of Starfleet Academy.

Plus, Star Trek: Khan, in issues 4 and 5, shows how Marcus found Khan and how he used Khan, forcing him to initiate his one-man war against Starfleet.

The  virtual collectible card battle game Star Trek: Rivals'' uses pictures of Marcus for card #81 "Admiral A. Marcus" and card #106 "Rogue Admiral A. Marcus".

External link 
 

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Starfleet personnel (alternate reality)
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Section 31 personnel