Cadis Etrama Di Raizel ( a.k.a Rai )
Rai is a very noble, elegant, and mysterious Noblesse. He has no knowledge whatsoever of the 21st century, and will often become lost and confused especially with regards to modern day technology (such as using a cell phone). He is often used as the manhwa's comic relief with his love of ramen and the errors he makes with technology. He has fallen into a deep slumber for 820 years, and had woken up in an abandoned building in South Korea. After seeing what most of the humans on the streets were wearing, Rai took on the uniform of a student from Ye Ran High School, which is under the administration of Frankenstein, and inadvertently followed the students there[2]. He currently resides with Frankenstein. He is shown to be extremely powerful with the ability of mind control, along with a technique called "Blood Field". Although he seems cold and apathetic on the outside, Rai has shown compassion towards human beings, though it is not known whether this is due to actual compassion or out of pride (an explanation of the past pointed towards pride for the Noblesse in general, but not Rai specifically). He always wears the Ye Ran High School uniform and a silver cross with chains on his left ear. In recent chapters it has been discovered that he is the "True Noblesse".
Frankenstein
Frankenstein is Rai's devoted servant. He supports Rai whole-heartedly and calls him "Master"[1]. He had tried searching for his master after Rai "disappeared" and had given up and went into hiding after failing to do so. Frankenstein is the principal/director of Ye Ran High School. He was stunned to find Rai in his school office after Rai had woken up and assumed the uniform of the school's students. Frankenstein is also immensely powerful, even though some of his powers had been sealed away by Rai. Frankenstein is a very cheerful person, but becomes quite serious and calculating when the situation calls for it, although during battles Frankenstein has shown somewhat of a sadistic side. He is also extremely organized and loathes messiness (Especially in his house). Like Rai, he is also very compassionate towards human beings, especially the students in his school. It seems like Frankenstein was an impressive scientist, who had also done immense amount of research, possibly on human modification before Rai "disappeared". All the research done was recorded down in his diaries, however due to unknown circumstances, it is now in the possession of Dr. Crombel and the organization.
List of other characters can be found here on wiki.
Source: wiki