A mysterious denizen of the island and antagonistic fraternal twin brother of Jacob. The Man in Black is able to take many forms, including the Smoke Monster and John Locke.
"You have any idea how badly I want to kill you?"
The Man in Black is in a seemingly never ending feud with his brother Jacob. The two were raised on the Island, by their adoptive Mother. The Man in Black tried to escape the Island, but his adoptive Mother thwarted his attempt. For revenge, The Man in Black killed her. When Jacob found out, he threw his brother in the Source, transforming him into the Smoke Monster. This started the rivalry between the two. However, because of his Mother's "rules" the two are unable of harming each other. The Man in Black must find a "loophole" in order to kill Jacob.
As the Smoke Monster, The Man in Black is a force to be reckoned with. It is immune to standard weaponry, but has a weakness for dynamite, as shown in The Exodus. It can move at incredible speeds, and while it appears to be intangible, The Smoke Monster can grab and throw its victims. The Man in Black can also take the form of anyone he chooses, most notably John Locke for the fifth and sixth seasons.