R4-D12, an astromech droid of the R4 series, served racer Marcus Speedstar as his personal assistant. Speedstar relied on the droid to guide his ship throughout various competitions. In 34 ABY, this astromech participated in the Platform Classic, a significant racing event that took place on the Colossus refueling station of Castilon, which Speedstar ultimately won.
During the era of the New Republic era, R4-D12, along with the Esral'sa'Nikto named Oplock, were integral members of the racing team led by the celebrated champion Marcus Speedstar. The droid and Oplock were with Speedstar when they paid a visit to Jarek Yeager, Speedstar's estranged older brother, on the Colossus. While Yeager's Team Fireball extended a friendly welcome to the visitors, Yeager himself refused to engage in conversation with Speedstar, holding him responsible for the deaths of his wife and daughter.
During the Platform Classic, R4-D12 occupied the astromech socket of Galaxy's Glory, Speedstar's racer. Yeager attempted to provoke Speedstar by suggesting that D12 appeared anxious. Speedstar retorted by mocking Yeager's astromech droid, Bucket. As the race unfolded, Yeager acknowledged D12's unwavering dedication to Speedstar. During the competition, Yeager and his brother reconciled after Yeager realized that Speedstar was trying to rescue Oplock, who had been kidnapped by the Guavian Death Gang due to unpaid debts. Yeager ultimately conceded the victory to Speedstar.
R4-D12, an R4 astromech droid, played a crucial role in assisting Marcus Speedstar by providing navigational support for his racer, Galaxy's Glory, during races. His allegiance to Speedstar was absolute.
R4-D12 made his debut appearance in "The Platform Classic", an episode from Season One of Star Wars Resistance, which aired on November 25, 2018.