An original character in the MCU, The Other has been a great contributor to Thanos and the Chitauri. He is played in the films by Alexis Denisof.
The Other makes his first appearance in this movie, where he oversees Loki's mission to steal the Tesseract from Earth and outfits the Asgardian with a scepter containing the Mind Stone. After the Chitauri invasion fails, the Other is seen telling his master of the Avengers. He warns him that to challenge the Avengers would be to "court death", a statement which makes Thanos grin.
The Other appears in this film as well, once again acting as a servant of Thanos. He is killed by Ronan the Accuser after an argument.