The British comedian and the 'Anger Management' star - who underwent a public meltdown last year - have struck up a friendship after working together recently promoting shows on network FX and the US actor came up with some special monikers for them to use.
Russell explained to The Sun newspaper: "I got an answerphone message, 'Brand, Genius One. This is Genius Two'.
"There were instructions to go to his house. There was him being Charlie Sheen - which was out of control - sat with a bunch who looked really on the edge.
"I think he's super-cool and funny as f**k."
It was recently claimed that 'Brand X' presenter Russell - who has previously battled addictions to drugs - has invited Charlie to join his yoga class.
A source said: "Russell and Charlie have been spending an increased amount of time together as they've been named by FX as the stars for their summer schedule so have done a lot of promotional work together.
"Russell has invited Charlie to join him at his yoga classes."