Josh Brolin's Thanos first appeared in Joss Whedon's The Avengers post-credits scene. He was revealed as the mastermind behind Asgardian Loki and the Chitauri's takeover on Earth. Further appearances showed his quest for power involving The Power Stone and his Infinity Gauntlet in The Avengers: Age of Ultron.
It's pretty much established how important Thanos' role is in the Marvel Cinematic Universe, but it isn't until now that we're learning how Marvel plans to map out his involvement in future films.
At the LA press day for Hail, Caesar!, Cinema Blend was able to ask Brolin about his future in the MCU. The 47-year-old actor claimed that Marvel will soon lay out all their plans for the Mad Titan.
So Kevin [Feige], Louis D'Esposito – who I've known for a long time, since he was a First AD that I worked with on Hollow Man with Verhoeven – and then the brothers… the Russo brothers. I get together with them next week, maybe the week after, and we're going through the whole thing. And I don't know anything at this point. I know a little, but, honestly, very little.
It's apparent from previous MCU films that Thanos is Marvel's most prominent character. The entire Marvel Universe basically revolves around his attempts at obtaining the Infinity Stones.
While the recent interview doesn't guarantee his appearance in any MCU film in the next few years, it's likely that we'll get a glimpse of him in 2017's Guardians of the Galaxy Vol. 2 or Thor: Ragnarok; either in the post-credit sequences or as a lead villain or a supporting one.
Avengers: Infinity War Part 1 will be released on May 4, 2018, while Avengers: Infinity War Part 2 is slated for release on May 3, 2019.