Inception Wiki

Cobb speaks to Fischer as "Mr. Charles".

Ariadne: Who or what is "Mr. Charles"?

Arthur: It's a gambit designed to turn Fischer against his own subconscious.

Mr. Charles is a tactic used by Dominick Cobb. The point of this tactic is to convince the subject that Cobb is a projection of their subconscious named "Mr. Charles."

This is accomplished by making the subject realize that they are in a dream and believing that Cobb is a special projection in charge of defending the subject's mind. By gaining the subject's trust, Cobb can then ally the subject with his entire team and turn the subject against his true projections.

The riskiest part of the Mr. Charles tactic is that it requires the subject to be aware that they are dreaming, causing the subject's projections to search wildly for the dreamer. If Cobb cannot adequately pull off the con, then the projections may quickly kill him and his team like during the Stein extraction job.