The Milkshake bartender has been working at the Shooting Star Milkshake Bar for an unknown time. The place was very dusty and old, very underpopulated and had not many customers. When Phineas Flynn and Ferb Fletcher's dad, Lawrence Fletcher, named the milkshake bar (actually a star) after them, they officially owned the place. When they came to the star that day, the bartender was the first to greet them, and they revamped the place. ("Out to Launch")
As Phineas and Ferb still own the asteroid, the bartender still will give milkshakes to the boys, and for free. During the middle months of that summer, Ferb drove by and was given a free one at the drive through. ("The Chronicles of Meap")
The alien bartender was a species that was purple and squarish, with two eyes above and below his mouth. He wore a classic milkshake bar hat and apron.