As Thor laid chained up as a prisoner in Muspelheim, he explained the journey which landed him in this captivity to a skull sitting beside him. The God of Thunder revealed he had been on a quest to find the Infinity Stones, following his enlightenment in Avengers: Age of Ultron. Of course, Thor never did come across the answers or stones he was seeking.
As close as Thor came to the stones, he was always a step behind one other being: Thanos. In the description of his journey, Thor said he constantly came up short of finding any Stones but, instead, would find paths of "death and destruction."
The description is a clear indication that Thanos or his Black Order had been to these areas ahead of Thor's adventure, either acquiring or at least seeking the same Infinity Stones. As seen in the Avengers: Infinity War trailer at Disney's D23 Expo and San Diego Comic Con, Thanos has quite a few Infinity Stones assembled by the time the next Marvel Studios ensemble flick rolls around.
At the end of 2012's The Avengers, Thanos' messenger tells him he would be required to "court death" should he challenge the humans. The sentiment earned a grin from the Mad Titan who would later appear in Guardians of the Galaxy, lending an Infinity Stone to Ronan the Accuser, having already given one to Loki. Of course, both of those mercenaries failed him, prompting Thanos' "I'll do it myself" line in the post-credits scene of Avengers: Age of Ultron. In the scene, he acquired the proper Infinity Gauntlet, with the original being ruled as "fake" in Ragnarok.
It seems likely Thanos has left that trail of death and destruction in his wake as he pursues the Infinity Stones and razing of multiple worlds and, now, he will have the precious Tesseract back thanks to Loki.
Thor: Ragnarok is now playing in theaters.