The Marvel Cinematic Universe (MCU) kicked off in 2008 with the debut of Iron Man, marking the beginning of a vast interconnected world of superheroes. The franchise's shared universe concept was teased in a post-credits scene in Iron Man, setting the stage for The Avengers Initiative. Over the years, the MCU introduced new characters, culminating in the epic battle against Thanos in The Infinity Saga. While many storylines were neatly wrapped up, some intriguing plot threads remain unresolved.

6 Bruce & Natasha

The Unfinished Romance

• Introduced in Avengers: Age Of Ultron

The hinted romantic arc between Bruce Banner and Natasha Romanoff in Avengers: Age of Ultron left a significant question mark. Despite moments of connection in subsequent films, the storyline was left hanging. With Natasha's demise, the resolution of this romance seems unlikely.

5 Asgard's Destruction

Guardians of the Nine Realms

• Featured in Thor: Ragnarok

Following Asgard's downfall and the relocation of its people, little is known about the state of the other realms. With New Asgard's focus on Earth, questions arise about the stability of the remaining realms in Asgard's absence.

4 Cross Bones

Mystery Employer in Civil War

• First appeared in Captain America: Civil War

The enigmatic employer of Cross Bones in Captain America: Civil War remains unidentified, leaving a significant loose end. The nature of the stolen biological weapon and its potential repercussions linger, hinting at future developments.

3 Red Skull

The Elusive Hydra Leader

• Revealed in Avengers: Endgame

Red Skull's mysterious whereabouts post-Infinity Saga raise questions about his future role. After fulfilling his duty regarding the soul stone, his potential return as a villain remains uncertain, adding an air of intrigue to upcoming MCU narratives.