Dr. List was the right-hand man of Baron Von Strucker, and acted as his representative at the gathering of HYDRA heads.
List first appears in Captain America: The Winter Soldier. After the fall of SHIELD, he and Baron Von Strucker discuss what will happen next.
In "Aftershocks", List gathered all the HYDRA heads together. He told them about how Daniel Whitehall had recently been killed by SHIELD. List thought that Sunil Bakshi was the best choice to replace Whitehall but all the other HYDRA heads wanted that position as well. List told the other HYDRA heads that whoever managed to destroy SHIELD for good would win Whitehall's position.
Later, Bakshi seemingly managed to escape from SHIELD custody. He called Octavian Bloom who told him to meet him at his mansion. Bakshi and Bloom spoke to List. They think that List and Strucker wanted to kill them. They realize that the other HYDRA leaders wanted to kill them and they have them killed.
In "The Frenemy of My Enemy", List had a meeting with Bakshi and Mike Peterson, posing as Bakshi's body guard. List told Bakshi that he wanted to capture Inhumans and experiment on them just like Whitehall did. List then flew to his HYDRA base in the Arctic.
In "The Dirty Half Dozen", List found out that HYDRA managed to capture Peterson and an Inhuman named Lincoln Campbell. List and Bakshi thought that the pair wouldn't survive the experiment. List ordered the experiment on Peterson and Campbell to begin.
List found out that SHIELD was approaching. He ordered their plane to be shot out of the sky. Unbeknownst to List, the SHIELD agents on the plane survived the explosion. A small team of agents led by Phil Coulson managed to infiltrate the base with Bakshi's help. However, List barely managed to escape.
In Avengers: Age of Ultron, List re-groups with Baron Von Strucker in Sokovia. The Avengers attack their base because Coulson gave Maria Hill the base's location and she gave it to the Avengers. Strucker and List put a shield up in the base but the Avengers manage to penetrate the shield. Iron Man finds List attempting to delete the file on the Twins. Iron Man shoots and kills List with his gamma ray.