Rex Tremendae (English: Tremendous King) is the Latin song that plays during the intro cutscene of Megalith, the final mission in Ace Combat 04: Shattered Skies. It is also considered as a musical prologue to Megalith -Agnus Dei-, which plays during the first part of the same mission directly afterward. Rex Tremendae is featured as track 12 of Disc 2 of the Ace Combat 04: Shattered Skies Original Soundtrack, and was composed and arranged by Keiki Kobayashi. The lyrics were performed by the Namco Hometek Choir.
- The lyrics are taken from eighth stanza of the Dies irae, a Latin hymn known for being used in the Requiem (Funeral Mass).
- "Requiem" is also used as the name for the track that plays when the player fails a mission in Ace Combat 04, either by crashing or not completing an objective.
- Rex Tremendae was used in Teaser 01 of Ace Combat Infinity.