Édouard was the alter ego of Jean-Michel Rivat, a pop songwriter who wrote hits for France Gall, Sylvie Vartan, and Stone et Charden, among others. Rivat took his parody of long-haired "beatnik" singers way over the top, as you can see from the above picture, but the music itself actually isn't too bad.
The main butt of this joke is, of course, psych superstar Antoine, avec ses cheveux longs et ses chemises à fleurs. "Les Hallucinations D'Édouard" is a straight-up cover of Antoine's signature song "Les Élucubrations D'Antoine" (which was itself a semi-cover of Dylan's "Subterranean Homesick Blues") with a few lyrical changes, of course. B-side "My Name Is Édouard," on the other hand, is more of a British beat parody, both musically and lyrically. But both songs are great to listen to whether or not you know what he is saying, non?