Check this out, especially:
https://unquietthings.com/the-incandescent-otherworlds-of-gervasio-gallardo/
And:
https://www.isfdb.org/cgi-bin/ea.cgi?Gervasio_Gallardo
https://en.wikipedia.org/wiki/Gervasio_Gallardo
"Born at Barcelona, Gallardo studied in Spain, working for several
Spanish advertising agencies, before moving to Munich, Germany in 1959.
The next four years he spent working for the Delpire Agency in Paris,
before travelling to the United States in 1963. Here he met Frank and
Jeff Lavaty, who represent his work to this day.
"In 1969, he was commissioned by Ballantine Books to create cover art
for their Ballantine Adult Fantasy series. He went on to be the most
prolific of their cover artists, creating a total of twenty-nine. Since
then, he has created at least eighteen covers for other authors,
including producing all of the artwork for his own release: The
Fantastic World of Gervasio Gallardo. Eventually Gallardo returned to
Barcelona to set up a studio. In 1977, 1978 and 1979 Gervasio Gallardo
was represented at the International Art Fair of Basel by Sala Gaudà art
gallery,[1] where he exhibited individually in 1976 and 1978 [2] and
which today has a large part of his work.[3]
"Gallardo has won numerous awards within Europe and the United States,
and has exhibited his work in Paris, Barcelona, and the United States."
Works
Gallardo's covers include works by:
Peter S. Beagle
George MacDonald
Hope Mirrlees
H. P. Lovecraft
Hannes Bok
G. K. Chesterton
Lin Carter
Edmund Cooper and Roger Lancelyn Green
F. Marion Crawford
Lord Dunsany
Clark Ashton Smith
Sanders Anne Laubenthal
H. Warner Munn
William Morris
https://www.google.com/search?q=gervasio+gallardo+books&sca_esv=8214f2fdfa3e48e1&udm=2&biw=1920&bih=915&ei=yZuFZ_D7HuatptQPzdepoQw&ved=0ahUKEwiwhP6i5_OKAxXmlokEHc1rKsQQ4dUDCBE&uact=5&oq=gervasio+gallardo+books&gs_lp=EgNpbWciF2dlcnZhc2lvIGdhbGxhcmRvIGJvb2tzSKgKUI0BWOkIcAF4AJABAJgBL6ABiwKqAQE2uAEDyAEA-AEBmAIBoAI6wgIFEAAYgATCAgQQABgemAMAiAYBkgcBMaAH6gM&sclient=img
(book covers - you have to scroll down a bit to see the cover for "The
Forgotten Beasts of Eld")
https://www.goodreads.com/author/show/2535132.Gervasio_Gallardo
(slideshow, 5:25 minutes)