The "Captain Marvel" trailer revealed a long missed character in the MCU. Agent Phil Coulson. And look at that hair. He has hair! How we missed this guy!
Some MCU Phase One spoilers below
In the Marvel Cinematic Universe he first appeared in "Iron Man" then made subsequent appearances in most of Phase One Marvel movies. In "Avengers" he was later killed by Loki, while attempting to prevent the God of Mischief's escape. Though his death inspired the Avengers to get their shit together and kick ass in the final act of the movie.
He would later get a starring role in the MCU-connected TV series, "Agents of SHIELD" where he has been, apparently resurrected. It's not clear if Phil's appearance in "Captain Marvel" would be his last in the movies, but it would be really great to see him in Avengers 4.