Nearly pretentious but early death metal so im going with just silly -
The Key by Nocturnus - The story follows a cyborg who travels back in time to the year 0 B.C. to assassinate Jesus Christ which leads to the destruction of Christianity (highlighted by the controversial track “Destroying the Manger”) and the creation of a modern empire.
Don’t know whether Richard Dawson’s past-present-future trilogy might qualify in this thread as pretentious (even though he’s a very unpretentious guy) but his Circle collab album Henki being all about plants should count at least
Rudimentary Peni - ‘Cacophony’ (about HP Lovecraft)
Neutral Milk Hotel - ‘In the Airplane over the Sea’ (Anne Frank). I’ll let others decide if it fails the pretentious test.
The first 4 Mastodon albums are all individually concept albums, but they are all grouped together under the concept of relating to the classical elements. Remission being fire, Leviathan water, Blood Mountain is earth and Crack the Skye is air.
All actually extremely pretentious, but they’re great records and the quality of the bands output fell of a cliff from there on so think they get a pass.