Prior to the formation of the Titans, Robin was the first junior protege to begin his crime fighting career at the age of 9. Years later, Kid Flash was taken in by his uncle Flash after Wally recreated "the accident" which gave him super speed, Aqualad would gain his position by defeating the Ocean Master, and Miss Martian traveled to earth with her uncle.
After many years of being sidekicks, the sidekicks were treated to "graduation" where they were inducted into the hall of justice, they were left alone, inspired by their heroism they decided to form a team of their own since they were still not on "League Level". In this instance, the Titans predecessor, the Young Justice was formed. They investigated a mysterious case a project Cadmus which led them to discover Superboy, Superman's clone and freed him. This led Superboy to join the their Team and announce to the League that the Titans were official, and built their HQ atop Mount Justice.
They inspired young heroes everywhere into joining including the first group of heroes to join, Starfire, Beast Boy, Raven and Cyborg, resulting in the birth of the Teen Titans. The Titans would build Titans Tower on Titan Island in the outskirts of Jump City. The Titans became world renowned, and as famous as the Justice League who handled the Universe on a bigger scale thanks to the Titans acts. Robin acted as the primary leader while the Titans remained under league supervision. Even while apart of the Titans many sidekicks remained at their Mentors side, while many Titans were simply affiliated with the Titans alone.
The Titans foundation grew as more and more young heroes began to join, forcing the Titans to spread out their base into four frontiers in the North, South, East and West. This was the time that Robin momentarily left the Titans due to his issues with Batman. The Titans soon fell apart after an attack from The Brain and his forces. The Titans were disbanded for years until Robin returned as Nightwing and collected the former members and newer super hero's into three sections of the Titans, including the Titans, Titans East and Titans West.
Eventually the foundation of the Titans had grown to be sturdy and organized enough for Nightwing to officially announce his retirement as a Titan. He chose his successor to be Robin, who would hold the responcibility of leading the Titans main branch.