Keroro is a sergeant of Planet Keron's Army, and the commander of the Keroro Platoon.
According to Earth's Gregorian calendar, Keroro's birthday is December 9.[1] His blood type is O. His age is not revealed in detail, but considering the fact that he knows Angol Mois (who is currently 2000 years old) from when he was a child, it can be presumed that he is more than 2000 years old in Earth years (Watanabe, Keroro's seiyū, has stated that he played Keroro as someone who was about 45 years old). However, this is questionable, as Keroro described himself to be a child when Nintendo started selling the Game & Watch systems in Volume 7, Chapter 56.[2]
The origin of his name comes from the Japanese onomatopoeia for the sound a frog makes ("kero").