Remathilis
Legend
1e didn't have that many fiends in modules. [sblock]Temple of Elemental evil has I think an Alu-fiend NPC running around. There are occasionally succubi as helpless shackled prisoners who will betray those who free them. Tomb of the Lizard King has a summoned vrock as a wandering monster in the tomb. The drow modules have some NE daemons. The joke module compilation Castle Greyhawk has Asmodeus and pit fiends in the 1st level module and Grazzt in a later one. There are the Orcus centered Bloodstone Path modules. Probably a few more but that's what I got off the top of my head.[/sblock]
Module S4 (Lost Caverns) had a bunch, including Baphomet. The Classic Spider Queen Module was loaded with demons *(in Lloth herself). There were a few more, but they were rare indeed.