Produced in Spain in 1975 by Cropan, this 80-sticker album — formally titled Descubre a tus Héroes Fantásticos — is one of the most historically significant Marvel card sets ever produced, and remains almost entirely unknown to English-speaking collectors. Illustrated by the celebrated Spanish comics artist Rafael López Espí, whose character portraits are considered some of the finest Marvel art produced in any country during the 1970s. The album was designed reversible: flip it over and it became a 'Wickie the Viking' album on the other side.

The Cropan album contains True Rookie sticker appearances for an extraordinary roster: Cyclops, Jean Grey, Iceman, Beast, Angel, Magneto, Professor X, Scarlet Witch, Quicksilver, Black Panther, Silver Surfer, Galactus, Ghost Rider, Iron Fist, Luke Cage, Shang-Chi, Hawkeye, Moondragon, Nick Fury, Punisher, Red Sonja, Falcon, Ka-Zar and dozens more — all predating their English-language card appearances.

Beyond the A-listers, the Cropan album ventured into genuinely obscure territory: Gullivar Jones (Victorian warrior of Mars), Solomon Kane (Robert E. Howard's Puritan adventurer), Killraven (Marvel's post-apocalyptic fighter), Doctor Spectrum, Kragonn, Phantom Rider, Demon Druid, Darkoth. Characters who would not appear on any English-language card for another decade received their first trading card appearances here.

The Cropan album was produced the same year as the 1975 Topps Comic Book Heroes Stickers — yet the two sets share almost no character overlap. Topps featured ~40 characters with gag captions. Cropan featured 80 characters with serious illustrated portraits, going far deeper into the Marvel roster. This was possible because Spain's publisher Ediciones Vértice had been printing Spanish-language Marvel reprints since 1969, giving Spanish readers encyclopedic knowledge of the Marvel Universe.

The Cropan set received an unlikely second life in 2000, when Spanish publisher Forum produced a booklet titled Galería de Personajes Marvel reproducing López Espí's original illustrations. However, two characters — Gullivar Jones and Talon — were omitted from the reprint due to licensing complications. Original 1975 Cropan stickers for these characters are therefore the only collectible representations of them in the album's publication history.

Original 1975 Cropan stickers were plastic-coated cromos — a Spanish sticker format thicker and more durable than typical paper stickers — inserted into small pastries and sweet products sold at newsagents and candy shops. The 2000 Forum reprint used flat printed cardstock and is easily distinguished from originals by texture and finish. Any original 1975 Cropan sticker in collector condition, plastic coating intact, is a rare find outside Spain.