possesseur ça n'existe pas.
On distingue propriétaire (owner) de contrôleur (controller)
A permanent’s controller is whoever put it into play unless the spell or ability that put the permanent into play states otherwise. Other effects can later change a permanent’s controller.
A spell or activated ability on the stack is controlled by whoever played it. A triggered ability on the stack is controlled by the player who controlled its source at the time it triggered.
Objects in zones other than in play or the stack have no controller. If anything asks for the controller of an object that doesn’t have a controller, use its owner instead.
Owner
The owner of a card is the player who started the game with that card in his or her deck or, for cards that didn’t start the game in a player’s deck, the player who brought the card into the game. (Legal ownership is irrelevant to the game rules, except for the rules for ante.) The owner of a token is the controller of the effect that created it. See rule 200.1a.
An effect can change a permanent’s controller but never its owner. (A few cards have the text “Remove [this card] from your deck before playing if you’re not playing for ante.” These are the only cards that can change a card’s owner. See rule 217.9, “Ante.”)
A card is always put into its owner’s library, hand, or graveyard, regardless of who controlled the card in its previous zone. See rule 217.1a.