Marvel’s Avengers: Infinity War is now available on Digital HD, and while fans are scouring through the film and the special features, the commentary track reveals a surprise cameo almost immediately. Director Joe Russo, who is featured on the commentary track with his brother Anthony Russo and writers Christopher Markus and Stephen McFeely, states right away that Kenneth Branagh lends his voice to the Asgardian who sends out a distress call, which is literally the first thing heard in the movie. The character is never seen, but director Joe Russo said Branagh’s involvement came very late.
“This was an amazing surprise, by the way. We had this idea very late in editorial, to ask the amazing Sir Kenneth Branagh to come in and do the opening distress call, over the logo, that sets the stage and carries us into the scene with Thor and Thanos and Loki on the arc.”
Source: IGN.com Infinity War Commentary Track Reveals Kenneth Branagh Cameo