The CGI used for Thanos is widely regarded as the best use of CGI in cinema history. The Mad Titan was menacing and often sympathetic as he took on the combined might of the Avengers. Below you can see how some of this was created.
Here you can see Josh Brolin making different facial expressions and how this was relayed onto the face of Thanos.
You can even see Thanos in motion pulling multiple expressions in this reddit post!
How about Thanos pouting/making the duck face?
Who knows what Josh Brolin got up to when he was creating Thanos? But it’s certainly interestingly to see how the villain was brought to life in these few pictures.
