The latest trailer for Thor: Ragnarok features a major Easter egg from the "Planet Hulk" Marvel Comics story.
As Thor prepares for battle in Sakaar's gladiator arena, he puts his helmet on during a shot which sees Chris Hemsworth's character from a profiling angle. On Thor's neck, we see a dark circle mounted.
This dark circle is an "Obedience Disk." The disks were used in "Planet Hulk" when the Hulk was taken prisoner by the Red King and turned into a gladiator. Eventually, the Hulk would go on to fight the Silver Surfer in a moment which would see the two characters call each other "friends" before having the bout. Thor: Ragnarok appears to be playing with the scene a bit, swapping Thor for Silver Surfer and calling the Hulk his "friend from work."
The disk is seen in live-action form in the recent "Revengers" promo for Thor: Ragnarok. It was not visible in the previous trailers. Whether this was a move to attempt preserving a spoiler or because the object was added in digitally since the first two trailers premiered is unknown.
Resisting Obedience Disks, in comics, would result in an electric shock and inability to use super powers. The Hulk nor Silver Surfer, two of the most powerful beings in the Marvel Universe, were able to resist their commands.
Though the Red King does not appear to have a presence in Thor: Ragnarok, Jeff Goldblum's Grandmaster looks to be filling the role very thoroughly. While speaking to ComicBook.com on the set of Thor: Ragnarok, director Taika Waititi stressed the influence the "Planet Hulk" storyline will have on this particular film. "[The Grandmaster is] the ringleader of the circus on Sakaar," Thor: Ragnarok executive producer Brad Winderbaum said. "But he's also a little bit of like a brutal dictator, although he's completely unaware. To him it's all good all the time."
As for whether or not the Hulk is wearing an Obedience Disk in Thor: Ragnarok, it hasn't been spotted yet, but it's a likely possibility.
Thor: Ragnarok hits theaters November 4, 2017. Advance tickets are available now wherever tickets are sold.