Robert Fischer, the mark for Inception
A mark is the target of a con, and in a dream the mark acts as the subject. If someone is trying to perform Extraction or Inception on the mark, they can enter the mind of the mark through the process of dream-sharing.
Once inside the mark's mind, a dreamer can create a dream space where the mark is the subject, filling the space with details and secrets from their own subconscious. An extractor can then either steal these secrets or perform inception by planting an idea and making the mark think it is their own.