His personality seemed to mesh well with Accord given there was a supposed partnership, or even friendship between them.
His power allows him to capture and torture individuals for information and as long as his targets would have no memory of what happened and he would face no consequences. He used this partially to gather information and partially as stress relief.
Coil had several plans to assist the Travelers with their main issue. But when these failed, such as getting the assistance of Panacea,
 he ultimately schemed to turn their situation to his advantage.
The chess-master was a pawn in a much larger game. He had to make promises and deals with powerful people to gain his abilities, and put himself into debt doing it. His civilian identity and potential importance were what allowed him to get his powers in the first place.
Accord considered Coil a friend, it is unknown to what extent this was considered mutual. However if an opposing faction ever reached out to Accord to for help against Coil any advice they were given would be slanted to give Coil an advantage.
Thomas is described as a skeletally thin man, taller than Grue.
As Coil, he wore a skintight black bodysuit with a stencil of a white snake curling around it, its head on his forehead, extending down the back of his head, looping and winding over his entire body with its tail at one ankle. A zipper was hidden in the snake, at his ankle. His mask didn't have eye holes. The fabric of the costume allowed him to see and breathe through it, but was an opaque black-gray to outside observers in all but the brightest light. The way it clung to his skin let you see his individual ribs and joints.
In his civilian identity, of Thomas Calvert, he had close cropped, coarse hair, trimmed eyebrows, thin lips and a cleft chin. He wore the body portion of a PRT uniform with an insignia stitched onto his sleeve.
Coil is arguably one of the most powerful supervillains in Brockton Bay. In addition to his power, he employs a variety of supervillian teams and independent supervillains; the Undersiders, the Travelers, Uber and Leet, Circus, Chariot, Trainwreck, and could hire Faultline's Crew or even cape mercenaries from Boston and New York as needed. He is also the head of a large mercenary force that he outfits with top-of-the-line gear including tinker-tech rifles.
Coil's power appears to grant him the ability to 'split' the world into two timelines and then collapse the timeline he likes less whenever he wants, "destiny manipulation". In truth his power allows him to mentally simulate concomitant timelines, or corcognition, until he dies in one of the simulations or he chooses to end one of the simulations.He can never have more then two. Once he makes his choice he essentially enters 'autopilot mode' and follows the actions he took in the simulation. Once it is over he is free to do as he wishes again. 
This power allows Coil to attempt different courses of action regarding a situation and then pick the timeline he wants to keep while retaining all knowledge from the other timeline. Much of his real world success ultimately hinged on this ability to create feed-forward loops; being able to test his plans in different permutations before acting upon them. Time moves forward in his realites regardless of what he does, this limits what he can actually do in a specific timeline.
Sources of "causality interference" interfere with his power, including most precognitives, meaning he can't make use of information-gathering powers again and again in different timelines.
Thomas was a part of the PRT's special forces. When the PRT received reports about Nilbog, his team was sent in to deal with the situation. He was one of the only two survivors of the following incident, the other being Emily Piggot.
At some point, Thomas found out about and approached Cauldron before he bought a superpower. It was expensive, forcing him to postpone his plans and spend years gaming the market in order to pay it off.
His plans so close to fruition he had to deal with Dragon and Defiant deploying their new mechanical suits to Brockton Bay. After paying a hefty sum to the Dragonslayers his hirelings were able to drive the suits out. He was then able to enact his endgame.
Faking his death in an attack at the mayoral debate he was able to disgrace Director Piggot and take over for her as Thomas Calvert. He did not account for Skitter being there in her civilian identity.
Skitter found out about his identity and confronted him. Calvert was prepared and made a clumsy attempt to kill Skitter. He almost turned Skitter's teammates against her, but failed due to Grue's power allowing them to uncover the deception. In the final meeting, Tattletale revealed that she bought out his mercenaries. Skitter than took a gun and prepared to shoot him. Coil assumed she wasn't a killer. Skitter bluntly told him "No. But I suppose in a roundabout way, you made me one." She than shot him in the head.
As a final spiteful gesture Coil released Echidna to plague the Undersiders and Brockton Bay.
↑ 1.01.1He canceled the reality where he stood at his pet’s bedside, found himself still at the computer. Best to leave the world where his pet wasn’t so tired, in case he wanted to ask more questions that morning.
The worlds he created weren’t real. They were little more than an especially vivid, accurate dream. To enjoy a whole separate world, free of any consequences beyond the ones he wanted? It would be unreasonable if he didn’t indulge in it. Anyone would, given the chance. - Excerpt from Interlude 8.x
↑Ah, but here’s my question – is it truly that bad, to murder, torture, maim, psychologically scar people, if it only really happens in your head? Or in a concurrent reality that never unfolds into long term consequences/a future?
I’m sure all of us have idly daydreamed about kicking some irritating customer/client/bosses ass, what it would take to get away with murder, etc. Is that truly so different from what Coil does to relieve stress?
I stress that this is a hypothetical, and should not be interpreted as my actual views. Just curious how people are interpreting it. -
Comment by Wildbow on Interlude 8.x
↑ 3.03.1Peanuckle said: I think Coil's biggest failing here is his desire to monologue, a classic villain mistake. If he had just ordered his men to shoot without bringing in Tattletale, then there wouldn't have been a problem. Then again, his claim to be able to deal with the PR hit was probably a bluff to destabilize Skitter. Being outed about his criminal career would probably cost him his position as PRT director.
There's a balance to be found. Haste makes waste, and just pulling the trigger and destabilizing things without stopping and touching ground involves risks. If Taylor's deadman's switch was real, for example, that would make rushing headlong into a disastrous scenario for Coil. He's spent all this time building up and securing his position, and he doesn't want to stumble at the last second.
Stopping and having a short discussion means you get to decipher just why things fell apart so you can manage things better in the future. Too easy to get into a situation where you're just doing damage control and you hastily plug a hole only to find that more of your subordinates are getting restless and entertaining the wrong sorts of thoughts.
Maybe not in this specific situation, but it would be Coil's overall mindset and personality.
As compared to the 'just about ego' monologue (though I imagine a smidge of ego was involved).
Peanuckle said: Even though Coil admits to torturing members of the Undersiders. I wonder if he tortured Lisa, but she toughed through it? More likely he grabbed Taylor or Brian since they're closer to the issue.
Why not all of them?
This would be why you compartmentalize the plan to take down the reality-splitting overlord. Talk it out, give everyone the key points, but don't tell Brian what Tattletale is doing, exactly.
Aside: I imagine if Tattletale got tortured in a Coil reality, she'd know it was a Coil reality and adjust accordingly. - Comments By Wildbow on Sufficientvelocity
↑ 6.06.1Perhaps worthy of a celebration. Coil maintained his own vices. It would be unfair to expect more of himself, when he had the unique talent he did.
It had certainly been an expensive talent. Even with his ability to game the markets in a way that clairvoyants and precognitives couldn’t detect, it had taken him years to pay it off. A maddening, frustrating endeavor, when he had already been thinking of plans he wanted to set in motion, having to postpone them. And he still owed a favor, even now, up to a week’s services. He couldn’t be sure if he was powerful and secure enough to fight back if they demanded too expensive a price, or too much of his time at a point critical to his plan. - Excerpt from Interlude 8.x
↑Nice post. Right on the mark. On the subject of why they don't always hand out powerful vials - they don't always know the power level of a given vial. They've got this landscape of Eden, they take pieces of it, make it into concoctions and feed them to people. One vial might have fantastic results in one situation and peter out or end up horrific in another. So they've spent the last 30 years figuring it out, trying to get as many vials to people as they can in the most constructive way they can. When they do get a set of powerful vials, they try to hold on to them and give them to the people they can make the most use out of. Often those are people in power (ie. the mayor of a town with a lot of capes, who then gives it to his son), people with access (an ex-PRT captain with the potential to be Director), or people with money. - Cauldron SOP
↑ 8.08.18.2Accord nodded, once. “As well as we might hope. We lost Coil, but the Undersiders may serve as a model in his absence.”
The gateway closed. Accord sat down on the end of the bed, then lay back, staring at the ceiling.
Coil had been the focus of the test, unaware. The man had also been Accord’s friend, the one who’d sold him the PRT databases. His death had been a tragic thing, on many levels. There were few men Accord considered worthy of being his friend.
Now it hinged on the Undersiders. They’d taken up Coil’s legacy, after a fashion, and just like Coil, their ambitions fell in line with Cauldron’s. The organization’s hopes rode on them and their decisions. Accord’s hopes rode on them: his twenty-three year plan, saving the world from the worst kind of disorder. In the end, they were responsible for billions. - Excerpt from Chrysalis 20.y (Interlude; Accord)
↑Coil's power doesn't create universes. It's essentially precognition in the present, purely thought based. - Wildbow on spacebattles
↑Think of it more like when he chooses a future to follow, his thoughts/actions automatically follow that script until it's done, and then he can think freely again. - Comment by Wildbow on Reddit
↑Here’s the thing about Coil’s power – he doesn’t control time in the worlds. Regardless of what he does, time passes in each reality.
So he couldn’t ‘play out the day’ to see if his plan would succeed and then go ahead & do it. He could simulate something close to it by rescheduling the debate and/or doing this at some other major event, then canceling the reality.
He could also attend the debate in one reality and stay home with his personal army in the other. If it doesn’t work out in the reality where he attends, he cancels it out and effectively never went. - Comment by Wildbow on Monarch 16.7
↑Coil's powers get discombobulated by other causality interference, which is why he can't just have Dinah give every answer in Coil-generated universes that he discards. -
Comment by Wildbow on Reddit