Armonia's appearance is that of a golden skeleton adorned with all manner of jewelry. He is always seen sitting in a heavily decorated throne made of skulls.
In Death Note 13: How to Read, Armonia is described as being a Shinigami that the King places a great amount of trust in. Because of this, many other Shinigami often approach him for advice. Being highly intelligent, he knows everything there is to know about the rules governing the Shinigami Realm. Armonia also sits on a throne and can sometimes be seen smoking. Takeshi Obata also describes him as being "conceited."
Armonia provides Sidoh with several scrolls describing the various rules that Shinigami have for interacting with humans, which Sidoh uses to guide his interactions with Mello in the Human World. The scrolls are not mentioned in the anime.
Obata stated that, for Armonia's body, he referenced Tibetan art that features skulls. He also used ideas stemming from Italian antique accessories that feature faces covered in jewels.