The list of Power Rangers' Red Rangers includes franchise legends Jason Lee Scott and Tommy Oliver, but neither of them was the most important Red Ranger in the saga. Jason was Power Rangers' first Red Ranger, the one chosen by Zordon to lead the team in Mighty Morphin Power Rangers. Tommy, the original Green Ranger, would become the Red Ranger in Power Rangers Zeo.
After Jason quit the Power Rangers, Rocky became the new Red Ranger. However, it was Tommy, the White Ranger, who led the team. Tommy would continue to lead the Rangers as the Red Ranger in Power Rangers Zeo and Power Rangers Turbo season 1. Despite Jason and Tommy's Power Rangers legacy, it was Power Rangers in Space who introduced the Zordon Era's true protagonist.
Power Rangers in Space's Andros was only introduced in 1998. However, in-universe, Andros had been a fighter since before Jason and Tommy became Power Rangers. Whereas the Mighty Morphin Power Rangers characters had regular lives before being recruited by Zordon, Andros was raised on a highly advanced planet and fought to survive since very young. Andros' sister, Karone, was kidnapped when they were both children. In addition, Andros's home planet, KO-35, was invaded by Dark Spector's forces. When exactly Andros became a Power Ranger is difficult to say, at least in the Power Rangers TV canon. That said, Red Ranger Andros was fighting for KO-35 during Power Rangers Zeo.
In the BOOM! Power Rangers comics' continuity, Andros was already the In Space Red Ranger during the events of Mighty Morphin. Regardless of whether that applies to the TV shows, Andros was mentored by Zordon and led a team of Power Rangers in space when Jason and Tommy were still fighting the monsters of the week on Earth. Whereas Zordon's Power Rangers teams were fighting to protect Earth, Andros was dealing with galactic events that could change the fate of the entire universe. When the Turbo Power Rangers went to space, Andros was noticeably more experienced and prepared to deal with Dark Spector than Zordon's Earthling pupils.
In terms of the Zordon Era, Andros was Power Rangers' true protagonist. Andros's story begins before that of the Mighty Morphin Power Rangers characters and ends with him killing Zordon in Power Rangers in Space's "Countdown to Destruction, Part 2." Power Rangers in Space begins with Andros crashing the Alliance of Evil's meeting, where pretty much every Zordon Era Power Rangers villain was present, by himself. Red Ranger Andros represented a threat to Dark Specter and his allies even when he did not have a Power Rangers team to lead. In Space was the culmination of Power Rangers' first five years, and Andros was the heart of it.
Related: What Happened To Each Power Ranger Between Mighty Morphin And Once & Always
After Power Rangers in Space, Andros continued to play an important role in the Power Rangers universe. The In Space Red Ranger returned for a crossover with Power Rangers Lost Galaxy, during which he had a rematch with the Psycho Rangers. Later in the Power Rangers timeline, Andros tracked down the remaining members of the Machine Empire and put together a team of Red Rangers to prevent Lord Zedd's Serpentera from being activated. In other words, Andros was one of the leaders of Power Rangers' Red Rangers crossover. Unfortunately, what happened to Power Rangers' Andros after "Forever Red" is a mystery.