Jacob and the nameless man in black are brothers. But this woman is most definitely NOT their mother.
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Jacob bids farewell to his brother and mother in this scene. They'll later be known as "Adam and Eve."
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The fake mother of Jacob and MIB stands in front of what will become the frozen donkey wheel. She holds the key to all Lost mythology.
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Perhaps the key scene in Lost history, The Man in Black kills his mother. Well, sort of his mother. It's a long story.
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Allison Janney plays a key role on the Lost episode "Across the Sea." Her character is seen here with Jacob.
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We got deep into the life of The Man in Black on the Lost episode "Across the Sea." He looks anything but happy in this scene from that installment.
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Lost Season 6 Episode 14 Quotes

Every question I answer will simply lead to another question.

Mother

MIB: So, do you want to play or don't you, Jacob?
Jacob: Yes. I want to play.