Agent Phil Coulson, the first S.H.I.E.L.D. agent seen in the MCU, wants to debrief Tony on his captivity and later helps Pepper go after Obadiah Stane.
Coulson is killed by Loki, and Fury uses his death to make the Avengers work together.
A small part in 2008 grew across Iron Man 2 and Thor until his death brought the team together.
Source: Wikipedia: Phil Coulson