All the R-Series are humanoid robots, wearing a soldier's uniform comprised of a jacket and assorted knee-high boots. The jackets have a similar style but different colors for each robot. They also all wear black pants and elbow-length gloves of different designs.
Each model has two horn-like components protruding from the sides of their head, except for Kelvis, who has golden hair clips where the components would be, and they most likely take the place of the horns.
Aside from Valghis, they all have a mechanical tail assorted to their uniforms that allow them to fly (Valghis can still fly without it).
Initially, the R-Series were only referred to by their unit numbers (R0, R1...). It was Princess Cecilia who first gave an actual name to R0, calling him Rodea. The rest of the R-Series became jealous, and asked Geardo to give them names as well.
Compatibility with the Key of Time (Spoilers!) Edit
This section contains spoilers for the end of Chapter 20
Each model has the ability to conceal at least half of the Key of Time. If both halves of the Key are combined, and the Key is pressed into the chest of one of the R-Series and then turned, it will open the R-Gate. It has only been confirmed that this can be done using Rodea, though Valghis claims he can also do this.