Certainly Nick Fury (Samuel L. Jackson) and Talos, the leader of the Skrulla (Ben Mendelsohn). Their participation was confirmed by Kevin Feige during Disney Investor Day 2020. And that’s most of the information we know about the series. It will be released during the fourth phase of the universe, and the first season will consist of six episodes. But what will his impact be on the rest of the MCU, what story will he tell, and who will be part of it? There are still no answers to these questions, but the announced casting may brighten the situation a little.
An actor in the 50-60 age group is wanted to play the main antagonist of the series. He will be joined by an actress aged 40-50, as well as a younger actress in the role of “important returning character”. For comic book fans, this data is enough to try and assign names and faces to specific people. The big bad series may turn out to be Dorrek VII, once the ruler of the Skrull Empire. A permanent female figure is to be a person who often shares the screen with Nick Fury, i.e. someone from his close circle. It could even be his comic book wife, Monica Chang, one of the three women who served as SHIELD director.
At the moment, these are just assumptions, fan-made theories. Will they prove to be true, we will find out when the management of Marvel Studios deem it appropriate. Until then, all that remains is to wait. And to make this time pleasant, maybe it is worth reaching for comics about the Secret Invasion event ? Reading is unlikely to hurt, although I do not guarantee that it will not increase the level of expectations for MCU production