Clyde the Fog Spirit is the main antagonist of the 2014 CGI special The Fog of Courage.
In life Clyde was a Caucasian man with large lips and teeth and black hair.
As a ghost he appears as mostly a large mass of iris-blue colored fog. He lacks a real body and only has long skinny arms with which to drag himself. He has a face in the front that resembles his face from when he was alive.
While nothing is said about how he was when he was alive, it's safe to assume that Clyde was deeply infatuated and in love with Cariana.
As a ghost he still maintains a now single-minded obsession with Cariana and the love locket, relentlessly pursuing it while repeatedly reciting her name. He seems to despise greed, becoming enraged when Eustace demanded an offer for the locket.
The only thing revealed about Clyde's life is that he fell completely in love with a woman named Cariana. He and Cariana later died under unknown circumstances and was buried with the love locket.
Clyde's angry spirit is awoken by Courage as he is digging a hole and finds his suction cup gun and the love locket. Courage brings the locket inside and shows it to Eustace and Muriel. Eustace and Courage consult Computer and learn that the locket is very valuable (to Eustace's glee) and that it will curse those who take it from the graves of two lovers. Eustace heeds no mind to the warning but Courage is worried he'll lose Muriel. That night Clyde comes to the Bagge Farmhouse in pursuit of the stolen locket. Eustace tries to scare him away with his truck but Clyde 'swallows' it and Courage (who had seen him approaching) rescues him just in time. Clyde knocks on the door and Muriel (thinking it's someone in need) opens it and he spreads through the house. Courage escapes upstairs into the attic and out the window with Eustace and onto the roof with Clyde in pursuit. Eustace demands Clyde "make (him) an offer" and enrages him, making him 'swallow' Courage and Eustace. Courage saws through the roof with his teeth and makes Eustace fall inside and throws the locket into Clyde's mouth. This appeases him and he recedes back to from which he came. Courage saves Muriel (who had been blinded by Clyde's body and was on the edge of the roof) just in time from falling off the roof with his suction cup gun. Eustace is in Clyde's 'grave' with the locket and he appears, saying his lover's name in a somewhat sensual tone.
Clyde is completely composed of fog and can 'swallow' things in himself and use his 'body' to blind people. He can also apparently touch things, seeing as how he knocked on the farmhouse door.