Captain America: The Winter Soldier.
From that point on, Agents of SHIELD has continued to reinvent itself around a core cast of SHIELD agents, led by a revived Phil Coulson (Clark Gregg). While audiences were already familiar with Coulson after making four movie appearances, the rest of the main cast introduced new characters to the MCU. His team consisted of Grant Ward (Brett Dalton), Melinda May (Ming-Na Wen), Leo Fitz (Ian De Caestecker), and Jemma Simmons (Elizabeth Henstridge), with Skye/Daisy Johnson aka Quake (Chloe Bennet) ing the team officially shortly after. Except for Ward, the rest of the cast have stayed with the show all the way through the seventh season of the series.
But, as time has gone on, how exactly Agents of SHIELD is connected to the MCU has been called into question. After references to the movies lessened in later seasons, the events of and arguably even contradicted) with the most recent seasons. This has led to many theories that Agents of SHIELD could use time travel to fix its place in the MCU timeline and possibly even bring back some familiar faces that previously left the show, such as Mockingbird or Ghost Rider.
Throughout the years though, Agents of SHIELD has featured a multitude of characters from MCU movies. There are some obvious names worth mentioning, but also a few that are easy to forget - and even one that many might not have noticed.
Phil Coulson
As the lead of the entire series, Agents of SHIELD likely wouldn't exist if it wasn't for Coulson. Audiences were first introduced to Coulson in Iron Man and he went on to appear in Iron Man 2 and Thor before dying in The Avengers. For the purposes of Agents of SHIELD, though, the series revealed that he was revived thanks to multiple experiments and some Kree DNA. He's been one of the main characters throughout the entirety of the series, but he died again at the end of season 5. However, Gregg returned as a Coulson lookalike named Sarge in season 6 and will play an LMD of Coulson in season 7.
Nick Fury
Samuel L. Jackson is the linchpin of the entire MCU and he's made multiple appearances as Nick Fury on Agents of SHIELD. His role on the show came during the first season of the ABC superhero drama, where he first appeared at the end of the second episode. Fury returned for the season finale after it was revealed Hydra had infiltrated SHIELD and helped Coulson to Captain Marvel.
Maria Hill
Cobie Smulders has made multiple appearances as Maria Hill during Agents of SHIELD. After working with Coulson in The Avengers, Hill appeared in the pilot episode of Agents of SHIELD and helped bring Coulson's team up to speed. She returned to the series after the events of Captain America: The Winter Soldier and helped them deal with the collapse of SHIELD. Hill's last appearance on the show came during season 2, where Coulson is the one who tells her where Loki's Scepter is located so the Avengers can find it at the beginning of Avengers: Age of Ultron.
Jasper Sitwell
Maximiliano Hernández returned as Jasper Sitwell on multiple occasions during Agents of SHIELD's first season. He was introduced working with Coulson in Thor and was by his side during The Avengers and Marvel's The Consultant One-Shot. His roles in Agents of SHIELD came throughout season 1, as he appeared in episodes 7, 15, and 16. Those were the only appearances made by Sitwell before the Winter Soldier killed him in Captain America: The Winter Soldier.
Felix Blake
Even though Titus Welliver didn't appear as Felix Blake in an MCU movie, he was introduced in one of Marvel Studios' One-Shots, Item 47. After this appearance, Blake appeared in three episodes of Agents of SHIELD. He made two appearances in the middle of season 1, with the second episode nearly killing him. But, he made a surprise return in season 3 as the leader of the Watchdogs, a superhuman hate group. Blake is still alive in the MCU, so he could potentially return in Agents of SHIELD's seventh season.
Peggy Carter
Hayley Atwell made a few cameos as Peggy Carter during Agents of SHIELD's earlier seasons. Her appearances in flashbacks coincided with ABC's investment in one of her Agent Carter co-stars will be in season 7.
The Howling Commandoes
Some of the Howling Commandoes also appeared on Agents of SHIELD. Neal McDonough returned as Dum Dum Dugan in the season 2 premiere of the series alongside Kenneth Choi as Jim Morita. Their cameos saw them reunited with Peggy Carter but the entire group featured in Captain America: The First Avenger was not present.
Doctor List
Henry Goodman returned as Dr. List multiple times on Agents of SHIELD after making his MCU debut in the post-credits scene of Captain America: The Winter Soldier. It was after the events of that movie that List appeared on the series for three episodes, providing more background on the character and what Baron von Strucker was working on. His final appearance in episode 19 of season 2 set up his return in Avengers: Age of Ultron.
Lady Sif
One of the more high-profile MCU returns featured on Agents of SHIELD was Jaimie Alexander reprising her role as Lady Sif. After appearing in two Thor movies, Sif returned in the first and second seasons of Agents of SHIELD. She first appeared hunting down the Asgardian Lorelei and returned in season 2 with her memory erased and hunting down a Kree alien. Despite Sif's role in the MCU, she hasn't returned to the movies since her stint on the small screen.
President Ellis
William Sadler returned as Matthew Ellis, the former President in the MCU, multiple times on Agents of SHIELD. His return came in season 3 after the events of Avengers: Age of Ultron, where he formed a SHIELD replacement team in Advanced Threat Containment Unit. His final appearance came when Mockingbird and Lance Hunter were kidnapped in Russia.
Gideon Malick
Powers Boothe made his MCU debut in The Avengers as a member of the World Security Council, but he returned in a bigger capacity thanks to Agents of SHIELD. The series provided a backstory for Gideon Malick, revealing that his loyalties lied with Hydra. He appeared throughout the third season of the show as an antagonist. Malick was murdered by Daisy Johnson in episode 17 of season 3.
Blackout
Marcus Daniels aka Blackout has also appeared in both Agents of SHIELD and MCU movies, but not like the rest of the characters mentioned before. Patrick Brennan debuted as Blackout in episode 18 of season 1 and returned for episode 19 as well. However, Brennan also was later cast in Captain Marvel where he played a bartender. It has since seemingly been confirmed that this is a younger Marcus Daniels by EVP of Production Victoria Alonso. This would make Daniels the only character to debut in Agents of SHIELD and then appear in an MCU movie after.