Four Great Dragons

The Four Great Dragons are four immensely powerful dragons working behind the scenes of the Digital World. They include Goldramon, Azulongmon, Magnadramon, and Megidramon. Note however that they are not all Holy in nature.

Digimon Adventures 02
Azulongmon appears after the crests (Courage, Friendship, Love, Knowledge, Sincerity, Reliability, Hope, and Light) released him.

Digimon the Movie:Hurricane Touchdown
Magnadramon appears alongside Seraphimon for a short amount of time.

Digimon Tamers
Megidramon appeared when Takato wanted Guilmon to digivolve to mega using his anger. Then Azulongmon first appeared when Zhuqiaomon attacked the Tamers.

Digimon Story Dawn/Dusk
Goldramon digivolves from AeroVeedramon, Megidramon digivolves from WarGrowlmon, and Magnadramon can be obtained by DNA Digivolving Angewomon with Lilymon.(More info can be found on their respective pages.)