Robert Downey Jr.'s Tony Stark is the godfather of the Marvel Cinematic Universe, ushering the franchise through the Infinity Saga until his death in Avengers: Endgame. As the MCU works its way through the current Multiverse Saga, the franchise still makes reference to the superhero who started it all, including in recent episodes of She-Hulk: Attorney at Law.
As venerated as he may be, Tony Stark was not always the hero that the world has grown to love. The character underwent a massive period of growth to become the greatest Avenger of all time and was aided by several important people in his life.
Howard Stark
Howard Stark was Tony's father with whom he had always had a troubled relationship. Rarely seeing eye-to-eye, the two Stark men were still estranged at the time of Howard's death, a discouraging reality that took Tony decades to surmount.
For all intents and purposes, the main reason the two Starks never got along was the fact that they were far too similar. However, as Tony grew older and wiser, starting a family of his own, he finally began to see life through his father's eyes, finding one last moment of connection with him after the two Starks are reunited during the time travel antics of Avengers: Endgame.
Obadiah Stane
Obadiah Stane was the first supervillain adapted by the Marvel Cinematic Universe, using the resources of Stark Enterprises to become the villainous Iron Monger. As Tony's pseudo-father figure after the death of Howard and Maria Stark, Stane's betrayal swept the rug out from underneath the young Stark.
Obadiah Stane may not have been the best villain in the MCU, but he certainly had a profound impact on Tony Stark. His betrayal forced Tony to learn to fend for himself, also picking up a few lessons about taking responsibility for his own actions along the way. In the end, it was Obadiah's scheming that inadvertently created one of the greatest superheroes the Earth would ever know.
Miriam Sharpe
Alfre Woodard has a short cameo in Captain America: Civil War, portraying Miriam Sharpe, a grieving mother who lost her son during the Battle of Sokovia. Sharpe confronts Tony, making it plain that she blames him for the death of her son.
He may have only had one interaction with Sharpe, but it was one that stuck with Tony for a long time. Her words influenced Tony's decision on the Sokovia Accords, prompting him to begin a new and more responsible phase of his life as a superhero, which spelled doom for the Avengers.
Natasha Romanoff
Natasha Romanoff first met Tony Stark in Iron Man 2 after being assigned to scout his talents for the Avengers Initiative. Working for Nick Fury, Natasha chose not to recommend Tony for the team, though the two would later serve side-by-side for many years to come.
Despite a rocky start to their relationship, Tony and Natasha would become good friends over the years. Though they would have their disagreements, Tony always respected Natasha's judgment, precisely because she was never afraid to call him out when he needed it. As a colleague, Natasha proved invaluable for sifting through Tony's ego and getting to his heart.
Dr. Bruce Banner
Of all the original members of the Avengers, Bruce Banner was undoubtedly Tony's best friend. The two were able to share scientific endeavors together, perhaps more than the MCU has even shown (as evidenced by She-Hulk's pilot episode), partnering on a number of projects during their long friendship.
Bruce had a way of balancing Tony out and offering him an outlet to vent about his problems. With Tony gone, Bruce is left without a best friend, though he himself may be embarking on his massive journey yet following a shocking reveal in She-Hulk's second episode.
Morgan Stark
Though some Avengers wallowed in their own guilt following the Blip, Tony chose to make something of the second chance he'd been given. He finally married Pepper Potts and, together, they had a daughter, Morgan, who is four years old at the time her father dies.
Everything changed for Tony when Morgan was born. Finally, he felt as though he had achieved his purpose in life, devoting his every waking hour to the daughter he never thought he'd have. His longing for actualization was finally satiated by Morgan's birth as Tony finally found his calling after so many years of searching.
Thanos
Thanos was undoubtedly one of the most terrifying villains in the MCU, whose conquest formulated the thrilling conclusion to the Infinity Saga. His presence loomed over Tony ever since the Battle of New York, making their eventual face-off in Avengers: Infinity War all the more significant.
Though Tony did not yet know who exactly he was preparing for, he spent much of his life working to protect the world from Thanos' return. It was this fear that inspired his creation of Ultron and that led him to take the fight to Thanos on Titan during the events of Infinity War. Ultimately, Tony would even make the ultimate sacrifice to keep Thanos from destroying all life in the universe at the end of the Battle of Earth.
Steve Rogers
Captain America and Iron Man make up one of the best superhero duos in the MCU. Their friendly (and sometimes not-so-friendly) rivalry carried much of Phase 3, as the two found themselves torn apart by the prospect of the Sokovia Accords.
Tony and Cap found themselves continually at odds, even when they were fighting on the same side. While this often proved destructive, their rivalry also served to improve each hero as they strove to prove the other wrong. Though Cap had once believed Tony to be a coward seeking nothing more than fame, Tony would prove him wrong by sacrificing himself to save the world.
Dr. Ho Yinsen
Dr. Ho Yinsen was a fellow captive of the Ten Rings terrorist organization during the time of Tony's imprisonment. He assisted Tony in creating his Mark I Iron Man armor, which allowed him to escape the terrorists. However, Yinsen died buying Stark time, pleading with his friend to not waste his second chance at life.
Yinsen's sacrifice altered Tony's entire outlook on life, helping him to realize the value behind every breath. Even over a decade later, Tony would quote his fallen companion, refusing to waste his second chance. Had it not been for Yinsen's heroic sacrifice, the world itself may have crumbled into oblivion under the might of Thanos, without Earth's best defender there to stop him.
Pepper Potts
Though Tony would forge many lasting bonds throughout the years, none would prove as strong nor as formative as that with Pepper Potts. His onetime aid turned successor and, finally, wife, Pepper was without a doubt the most important person in Tony's life long before they were married and had a child together.
Pepper was the only person who could bring out the softer side of Tony Stark, seeing through his brash veneer to the vulnerable man beneath. It was in Pepper's name that Tony fought many of his greatest battles, saving the world for her. In the midst of the chaos of Tony Stark's life, there was always Pepper to fight for.