While Agents of Shield
features a strong ensemble cast, Agent Phil Coulson
is undoubtedly the main character of the show and the reason for its existence in the first place. Unless the character returns in a future McU film, the series finale marks the end of his story and the last time the character would appear in the franchise.
Related: Agents Of S.H.I.E.L.D.: Every Main Character, Ranked By Intelligence
Each new season has brought new elements to the character, evolving him into the person he is at the very end by changing both the way the audience views him and how he views himself.