Origin: The Man in Black may have impersonated Ben's mother to lure him into the jungle. Ben may also have first encountered him in his monster form.
Since Then: As leader, Ben believed he had the power to summon the monster. The Others went to it for judgment. After the Man in Black took Locke's form, he led Ben to the Temple and took Alex's form, demanding his obedience. He then convinced Ben to kill Jacob for him. Ben appeared to ally with him later on, offering to kill people for him.
Origin: Claire had heard about the monster, but she didn't see it till it's arrival at the Barracks. It then attacked the men who'd just been firing rockets at her house.
Since Then: The following evening, the Man in Black approached Claire as her father, Christian, when she was in the jungle. She left Aaron behind and followed him to Jacob's cabin.
He kept her company over the next few years; the Others referred to this as claiming her and infecting her with the sickness. Claire changed considerably during this time, becoming more aggressive and less stable. The Man in Black told her that the Others had taken Aaron, justifying this by saying the hatred helped sustain her. He eventually began appearing to her simply as her "friend" rather than as her father, and Claire realized that he had been merely impersonating Christian earlier.
Once Jacob died and the candidates arrived on the Island, the Man sent Claire to warn the Temple of his arrival. Kate joined his group soon afterward, and he separated the two when Claire attacked, slapping Claire to quiet her. Claire learned she was not a candidate and feared he did not need her, but the Man in Black assured her that he did. Kate convinced her nonetheless to try to escape with her, an act that the Man seemed to later forgive. When the candidates boarded a trapped submarine, the Man held Claire back. But he abandoned her soon after to kill the sub's survivors.
Origin: The two brothers lived together on the island till the Man in Black went to the other side to live with his people.
Prize: For The Man In Black it was leaving the island. For Jacob it was to protect the island which meant he had to keep his borhter from ever leaving and "spreading his evil".
Fuel: They met regularly over the next years. When the Man in Black killed their Mother, Jacob cast him into the Heart of the island, transforming him into the smoke monster. The two spent the next couple thousand years debating the nature of humanity and each seeking a loophole to let them kill the other. The Man in Black eventually succeeded, but Jacob's ghost continued to visit him, warning him against harming Jacob's candidates.
Resolved: No, The Man In Black convinced Ben to murder Jacob however Jacob's candidates were able to keep The Man In Black from leaving the island and were eventually able to kill him.
Origin: The Man in Black, in his smoke monster form, chased Kate through the jungle on her first day on the island.
Since Then: Kate met him again in his monster form on several other occasions, including after she gathered dynamite from the Black Rock and while she was handcuffed with Juliet. She met him again years later after he took Locke's form, and he tried to gain her sympathies, talking of his "crazy" Mother. Kate tried shooting him after he killed Sun, Sayid and Jin, and she later succeeded.
Origin: Locke and the Man In Black first encountered each other when Locke was hunting for boar. The Man In Black (in his smoke monster form) approached Locke, something Locke would later describe as beautiful.
Prize: For The Man In Black, the prize was manipulating John until his death so he could use his form to kill Jacob and get off the island. For John, he was simply searching for his purpose in life.
Fuel: The Man in Black relationship with Locke was one of constant manipulation. After their first encounter, the Man attempted to pull Locke into a hole while in his smoke monster form, likely to infect him with the sickness. Locke would have gone willingly, but for Jack and Kate's intervention. Locke next saw the monster when the Man in Black attacked Eko; Eko's dying words were to tell Locke that he was "next". The monster continued to intrigue Locke, and when he managed to interrogate Ben, he only asked as to its nature. Ben claimed ignorance, but Locke soon later saw saw the monster attack the freighter's mercenaries, apparently at Ben's bidding.
Locke first heard the Man in Black speak when in the cabin. The Man in Black asked Locke to help him, angering Ben, and moved objects around the room. During his next visit to the cabin, Locke met the Man in the form of Christian. The Man told Locke to move the island, and when the two next met at the frozen wheel, he chastised Locke for letting Ben move it instead. He also confirmed to Locke that he would have to die - a fact Locke had first heard from Richard, who'd in turn heard it from the Man in Black.
After Locke died and his body was returned to the island, the Man In Black took his form to manipulate Ben into killing Jacob. After his true identity was discovered, he continually insulted Locke and everything that he stood for, yet he continued to adopt Locke's persona, passing off Locke's memories as his own.
Resolved: No, Locke died before he realized the Man In Black's manipulation. Jack, however, took the position Locke left and in fought in his memory.
Origin: Miles first saw the Man in Black, in his monster form, when Ben summoned in to fight the mercenaries at the Barracks.
Since Then: Miles later spent three years working for security at the DHARMA Initiative, during which he may well have encountered the monster. Afterward, he saw it again during the Temple massacre. When Hurley soon after suggested talking to "Locke", Miles refused, recalling the destruction he'd seen. He instead joined Richard in seeking to destroy the Man in Black's means of escape. When they seemed about to meet it again, Miles again took off in fear.
Unlike any other of the final main characters on the island, Miles never met the Man in Black in his human form.
Origin: The Man in Black recruited Richard as soon as he landed on the island to kill Jacob.
Since Then: Richard chose instead to work for Jacob, and he announced his decision to the Man in Black. Years later, after taking Locke's form, the Man knocked Richard out and again asked him to join him. Richard refused and began advising candidates to refuse him too. When his suicide attempts failed, Richard gave up and called to the Man in Black, asking to join him after all. He didn't end up joining him though and instead sought to destroy his means of escaping the island.
Origin: The two spent months on the island together, but Sun left before any encounter.
Since Then: When Sun returned, she saw the Man in Black, as Christian, in the old DHARMA processing center. He told her to wait for John Locke and returned shortly after - as John Locke. She followed him for some time because he claimed he knew how to reunite her with Jin. She eventually, however, learned that he was not Locke at all.
Sun entered the Temple while the monster was attacking and then left right after. Some days later, the Man in Black approached her in her garden, offering his hand and a new promise to bring her to Jin. She fled, not trusting him. When she and Jin were later together in a cage, the monster came to help break them out. Sun followed him to Widmore's submarine, where she dies, as he'd been planning.
In Sun's flash sideways, she caught sight of Locke when recovering consciousness and briefly mistook him for the Man in Black.
Origin: Windmore encountered the monster during his years as the Others' leader
Since Then: Widmore didn't understand what the monster was during his tenure. Years after he left the island though, Widmore said Jacob visited him and recruited him to fight the Man in Black. Widmore piloted a submarine to the island, set up a sonic fence to block the Man in Black and raided the Man's camp. And he brought a weapon against the Man in Black - Desmond. The two faced off on Hydra Island to no effect. They met again some days later in Ben's house, and the Man threatened Widmore into explaining Desmond's purpose.