- "Anyone have a good day today? No? Didn't think so. Me neither. Can any of you remember your last good day? I know we have it good here in the Commonwealth... I know it's better than whatever we had before we got here. But don't you see how much better this place could be? Day after day... we sweat and toil and grind... why? Do any of you like risking your lives for Governor Milton and her friends? I thought not. So why do we let them stay in power? Their power... is us. We see them sitting on their perch, looking down on the rest of us. It doesn't have to be that way. We can install new leaders... better leaders. We could do it quickly and peacefully, we could..."
- —Mercer trying to rally to the Commonwealth Military to overthrow Pamela Milton.[src]
Little is known about Mercer's life prior to or as the outbreak began, other than he served in the U.S. Military as a Marine and was on leave before the apocalypse started.
At some point in the apocalypse, Mercer encountered a network of communities called the Commonwealth which he subsequently joined; due to his military background, he was placed in the Commonwealth Army and rising to the position of Chief Officer. He also was appointed by Pamela Milton as a personal bodyguard for her and her son Sebastian.
Mercer is watching over Sebastian who is on a date with Kayla. Once walkers got too close to them, Mercer saves them, only for Kayla to call Mercer a pervert and walk back to the Commonwealth; Sebastian then yells at Mercer for ruining his date. Mercer is later talked down to by Pamela and ordered to change, promising they will discuss it later after talking with a new group of survivors from a settlement called Alexandria. In the officer's locker room, Mercer is talking to George about his frustration over how both Pamela and Sebastian belittle him and do not show him the proper respect; when George suggests they overthrow Pamela, Mercer voices his agreement to the plan.
However, a member of the Alexandrian group named Siddiq overhears them. Both Mercer and George see through Siddiq's weak attempts to convince them otherwise, but Mercer keeps George from attacking the man. Seeing him as a visitor to the Commonwealth, Mercer brushes the previous statements off as nothing but them blowing off steam and expresses gratefulness to how Pamela took them in. However, he does caution Siddiq that if he ever meets Sebastian, what they said about him being an asshole IS true.
Mercer later sees Sebastian push several members of the Alexandrian party and slap Elodie. He goes to disarm Juanita after she gets into a fight with a few officers, but does nothing when Sebastian orders the survivors banished for threatening him. Mercer sarcastically asks if that includes everyone who was watching, pointing out Sebastian provoked them first. After Mercer admonishes Sebastian for going around slapping people for no reason, the latter slaps Mercer as well; this angers Mercer, who throws a menacing glare at Sebastian and causes him to quickly back down.
Pamela later requests Mercer to accompany her for the trip to Alexandria. While traveling, he is asked by Pamela on what he thinks about the group of survivors; Mercer remains apprehensive but does notice how useful Eugene could be. Mercer remains close to Pamela as she formally gets introduced to Rick Grimes, the leader of Alexandria. When Rick volunteers to give Pamela a tour of the community, Mercer goes along with her.
During the tour of the nearby communities, they soon encounter a herd and Mercer reluctantly agrees to help drive the herd away; as Juanita expresses some worry, Mercer tells her to stay close to him. At the same time Juanita informs Mercer about Pamela's wagon moving closer to observe the herd, several walkers immediately surround Juanita and knock her off her horse; Mercer immediately goes back to save her. After the Militia arrive to clear up the stragglers, Mercer is caught by surprise when Juanita kisses him in gratitude for saving her. After Pamela expresses amazement, Mercer looks for an apology for needlessly putting both Juanita and himself in danger; Pamela gives a halfhearted one and walks away, causing Mercer to scowl at her.
En route to the Hilltop, Mercer asks Rick if the road they are travelling on connecting all the communities is safe. Mercer goes on to partly explains the class system in the Commonwealth, along with how he used to serve in the military as a Marine. He inquires if they follow a similar method of assigning specific tasks and is surprised when Rick responds in the negative. When Rick goes on to describe how no one is bound to their previous roles and everyone contributes in Alexandria (as well as everyone in their trading network), Mercer ponders it without giving a response. When they arrive back at the Commonwealth, Mercer is stunned to see it in the middle of a riot and goes to help disperse the mob. When Rick goes to help clean up the Commonwealth, Mercer is surprised and glad to see he managed to convince Pamela to help as well.
Later, Mercer and Juanita have sex and when prompted, he says what they have is more than just a casual one. He later helps bring Dwight to a cell after he assaults a fellow officer and stands watch when Rick visits him. He overhears them discuss how the class system in the Commonwealth is wrong and needs to be improved; silently agreeing with them, Mercer reveals himself and tells Rick that he, not Pamela, is the leader the Commonwealth really needs. After a mock hunting trip led by Pamela (who barely participates), Mercer reiterates to both Dwight and Rick how it is all for show. Dwight agrees that change is needed for the Commonwealth, while Rick is still uncertain.
After Dwight is killed due to Pamela's actions (and the resulting speech by both her and Rick), Mercer scowls at how Rick is still siding with Pamela. He goes home and is shocked to see Juanita packing. After hearing how she does not do well with confrontations, Mercer is saddened but understands her reasons. Venting his overall frustrations while killing some walkers, he is approached by Laura with a request to revolt against Pamela and install a new leader. Liking the idea, Mercer proposes it to George and the other officers later that day; however, Lance overhears him and expresses his dismay at Mercer. Looking for support, Mercer is shocked to see none of the other soldiers side with him and is promptly arrested.
Mercer is later visited by Pamela who expresses disappointment with Mercer's line of action and questions his loyalty. Having had enough, Mercer finally unloads on Pamela, furiously pointing out how both her and her son treat him essentially like a whipping boy and a slave. He mentions how she is not a leader, but a wannabe queen that does not care about the lives of anyone except her own and he wasn't going to wait until she tried appointing her "shit-for-brains son" as her successor. When Laura comes and visits him, Mercer sarcastically greets her but is confused to see her smirking. Suddenly, the back of his cell explodes and Mercer is showered with rubble and debris. He is glad to see George is there too and accepts his explanation for not siding with him earlier. Having his men seize Lance, Mercer begins scouring the area for Pamela. However, a mob of Commonwealth citizens appear and call Mercer a tyrant and fascist. After shooting in the air to disperse the crowd, Mercer spots Rick approaching. Finally breaking down, Mercer sees that he will not be seen as a benevolent leader but the Commonwealth might choose Rick instead.
He reveals that Pamela is only nice to those she views as being part of the elite class and everyone else as expendable, while Rick sees the value in everyone. After hearing Rick reluctantly refuse the offer (stating the Commonwealth needs more time to know him) Mercer says that is a luxury they do not have. Rick offers to get Pamela and since Mercer has not killed anyone, there is still time; just then, Eugene and Stephanie inform them of a rapidly approaching herd. Mercer is alarmed to hear Pamela pulled back the outer guards for her protection and goes to mobilize the soldiers. After the soldiers (along with the Militia) save the Commonwealth and clear out the herd, Mercer sees Pamela approaching with an army of her own from Greenville and hears her order for the army to attack.
This list shows the victims Mercer has killed:
- Numerous counts of zombies and unnamed people
Mercer is Sebastian's personal bodyguard and the two have a very poor relationship. Sebastian is verbally abusive to Mercer, despite Mercer saving him from numerous counts of walkers which resulted in him ruining Sebastian's date with Kayla. Mercer likewise hates Sebastian strongly, but holds his tongue when around him. Sebastian looks down on Mercer, and possibly views him as expendable.
- "Did you say loyalty? Where's your fucking sense of loyalty? I was never more than a glorified errand boy for you. I was a babysitter. I was a chauffeur. I was your whipping boy. You put me in danger more times than I can remember, and you never seemed to give a fuck all the times I nearly died for you. You're not a leader, you're a fucking wannabe queen, and I'm not waiting around until you try to install your shit-for-brains son as your replacement."
- —Mercer to Pamela upon having his loyalty questioned.[src]
In Issue 187, Mercer loses all respect for Pamela and goes as far as trying to rally the Commonwealth Military to overthrow her. When confronted by Pamela about his actions, Mercer lists all of the times he risked his life for Pamela and how she didn't care. He calls Pamela a "wannabe queen", and seems disgusted by her leadership.
Mercer and George have a good relationship and often confide in each other. They go as far as conspire to overthrow Governor Milton, though they claim they are just blowing off steam when doing so. When Mercer tries to rally the soldiers to overthrow the governor, however, George refuses to join him, though he is visibly ashamed of doing so. George ultimately does join the rebellion, and helps Mercer escape from jail, explaining that, back in the locker room, he didn't know which soldiers were loyal to them.
Mercer and Princess are on good terms. She is romantically attracted to Mercer, when he saves her from a herd of walkers she kisses him.
Later on, after arriving at the Commonwealth, Juanita and Mercer have sex. Their conversation afterwards shows they feel something for each other. Mercer mentions that he really likes listening to Juanita talk and that it's definitely not a casual thing. They kiss and Juanita says that her life is getting better every day now, to which Mercer smiles happily in response.
- "I'm in over my head here--I'm drowning. I can't do this without you--I need your help. If they won't choose me over Governor Milton--maybe they'll choose you."
- —Mercer inviting Rick to help him with his coup.[src]
- "If you're pissed off about how fucked up things have gotten around here, then it would seem we're both frustrated by the same thing. Any interest in putting that frustration to good use?"
- —Laura proposing an alliance to Mercer.[src]
- "If I knew, I'd be with her, you fucking moron!"
- —Lance to Mercer, upon being questioned regarding Pamela's whereabouts.[src]
- Mercer is the third known survivor who was a member of the military before the apocalypse occurred, along with Abraham Ford and Dwight.