In the comic book arc of the Infinity Gauntlet, Thanos had an underling in the form of the demon Mephisto. Mephisto appeared to be serving Thanos, but actually had his own agenda and wanted to use his position to deceive the Mad Titan and take the Infinity Gauntlet for himself. Mephisto isn't in the Marvel Cinematic Universe and probably won't ever be and, given that Mephisto's deception plan sounds exactly like something Loki would do, Tom Hiddleston's character could replace him in the underling role. The wheels are already in motion for this to happen, as Loki served Thanos in the first Avengers movie. However, he failed and the Other told Loki that Thanos would punish him for that. However, Loki still hasn't been punished but he has managed to manipulate his way to Asgard's throne - Asgard being where the Tesseract is being stored. Loki, therefore, may well be planning to retrieve it for Thanos in order to spare his life, with the ultimate aim to claim the Infinity Gauntlet for himself.
