Yesterday we had an interesting EDH game where someone cast Bribery on a creature, and later on in the game, that creature got Ray of Command. Now the question is, who gets the control of the creature after Ray of Command gives it back?
The player who cast Bribery is the default controller of the creature, since it entered the battlefield under that player's control. Ray of Command creates a control change effect with a set duration, but this doesn't change who the default controller is. When it expires, control returns to player who previously controlled it.
The same would be true if one player controls a creature due to a continuous effect, such as with Blatant Thievery, and another player casts Ray of Command on that creature later. Ray of Command's effect applies on top of the other control effect and effectively overwrites it, but doesn't make the other effect go away. When Ray of Command's effect ends, the creature goes to whoever should control it based on any other control change effects that are present.