Royal Knights - There are 13 Royal Knights in total not all have been revealed as of yet (11/13). They protect the Digital World in the 'common good' even though that good isn't always right as we saw in Frontier, Savers and 8th Movie. No matter what they do they follow Yggdrasil's orders.

Alforce V-Dramon (Ulforce V-dramon) - Depending on which variation of his name you use Alforce for Alpha Force, Ulforce for Ultimate Force, V is short for Victory and Dra for Dragon. The only variation of this monster is show in the V-Tamer Manga Alforce V-dramon Zero. But more recently he has been revealed in Digimon Savers.
Alphamon - Alpha is the first letter of the Greek Alphabet, he is the 13th Royal Knight and is said to be the leader. He is shown in the X-Evolution Movie, Chronicle Minis and D-Cyber Manga.
Dukemon (Gallantmon) - Dukemon's name is based on the name Duke. He is the 'peace' maker in X Evo and fights Omegamon to stop him carrying out Yggdrasil's plan. In Savers he fighs with fellow Knight Sleipmon.
Dynasmon (Dunusmon) - Dynasmon appears in Digimon Frontier and was one of 2 intros to the Royal Knights. His data was revived by Lucemon to do his bidding. In Savers he attacks the human world.
Lord/Rhodo Knightmon (Crusadermon) - Lord Knightmon also appears in Digimon Frontier as was the 2nd of the intros to the Royal Knights. Like Dynasmon his Data was revived by Lucemon. Again attacks the human world and gets returned to a Digitama by Mirage Gaoga Burst Mode.
Magnamon - his name means large. He is seen as a Royal Knight in the X-Evo movie but was seen in Adventure 02 as an Armour Evolution. he warns Yggdrasil of Omega + Alpha's coming in the movie.
Omegamon (Omnimon) - Omega is the last letter in the Greek Alphabet. He is determinded to see Yggdrasil's plan to go through but when Alphamon shows him the way he doesn't. We first see Omegamon in the 2nd Digi movie.
Cranniumon first appeared in Savers and like the other Knights follows Yggdrasil's order and fights with Masaru + Shine Greymon.
Slepimon is in Savers as the 'good' Royal Knight refusing to undertake Yggdrasil's orders and as the emisary of the Digital World teamed up with Satsuma as Kudamon. He fights with Dukemon and goes Kamikaze, last seen in an explosion....
Duftmon was revealed as a Royal Knight in Savers, follows Yggdrasil's orders to attack, Rose + Raven Burst Modes return him to a Digitama
Examon is the latest to be revealed as a Royal Knight.
Episode Guide
Other Characters
XROS WARS (Young Hunters)