Not just glam rock, but other musicians adopt various degrees of "persona" for a show. It seems to me the purpose of which is to add some visual performance element to accent the music.
Off the top of my head:
-- Ian Anderson from Jethro Tull played the "Aqualung" character
-- Roger Waters played "Pink" from "The Wall" album.
-- Maynard from "Tool" often plays characters from their songs while singing
-- Les Claypool of "Primus" always wears a costume of some kind on stage.
--And "Bucket Head" - whatever that's about.
-- Countless female pop singers like Madonna or Lady Gaga.
Off the top of my head:
-- Ian Anderson from Jethro Tull played the "Aqualung" character
-- Roger Waters played "Pink" from "The Wall" album.
-- Maynard from "Tool" often plays characters from their songs while singing
-- Les Claypool of "Primus" always wears a costume of some kind on stage.
--And "Bucket Head" - whatever that's about.
-- Countless female pop singers like Madonna or Lady Gaga.