Nightwing is often viewed as the definitive Robin and, by definition, Batman's most iconic sidekick, but further proof can dispute such an idea. Dick Grayson was introduced into the DC Universe as both the first Robin and Batman's first sidekick.
With Dick being the first Robin, it's understandable why so many people associate him most with his early days, but he's been so distanced from that role by now that it's hard to justify him as the definitive holder of the Robin mantle. Nowadays, readers are more likely to associate Dick with the name Nightwing than with Robin. Even as far as being Batman's sidekick, he's been long removed from that role as he's spent much of the past few decades going solo. Plus, prior to becoming Nightwing, Dick had already distanced himself from Batman for quite some time as a member of the Titans.
If anyone has reason to be considered the definitive Robin, it would be Tim Drake, who became the third Robin in 1989 and maintains the role to this day, save for a brief stint as Red Robin. It was as Red Robin that Tim mentions in Grant Morrison, Ryan Sook, and Pere Pérez's Batman: The Return of Bruce Wayne #5 that, "I was Batman's partner longer than anyone else."
Tim Drake is Actually Batman's Longest Serving Partner
It's a well-known fact that Tim Drake is the longest Robin, but to hear it put in of him being Batman's longest-running partner puts things into a new perspective. Other Robins like Jason Todd, Dick Grayson, and even other sidekicks like Barbara Gordon's Batgirl started their solo adventures far earlier than Tim ever did. Even as Tim maintains his solo adventures, he still remains Batman's primary sidekick in current DC continuity. A lot of audiences who grew up watching and reading Batman's adventures more recently are going to recall Tim Drake as Robin more than Dick or anyone else. Although Damian Wayne is the most recent Robin, his run with the "R" on his chest is still relatively new while Tim has maintained the Robin mantle for more than 30 years now.
Beyond just confirming that he is the definitive Robin, Tim Drake pointing himself out as Batman's longest-running sidekick feels interesting considering that it wasn't that long ago that he expressed a newfound desire to claim Batman's mantle in last year's Batman: Urban Legends #6. In being physically closer to Batman than any other sidekick, Tim has also worked under his tutelage longer than any other sidekick. Batman has worked more closely with Tim than with other sidekicks to refine his skills as a detective and a fighter. As such, there's an argument to be made for this former Robin to be better suited to one day precede Bruce Wayne for the Batman mantle than even Nightwing.
