Video Games Encyclopedia

Isometric platformers present a three-dimensional environment using two-dimensional graphics in isometric projection. The use of isometric graphics was popularized by Sega‘s arcade isometric shooter Zaxxon (1981), which Sega followed with the arcade isometric platformer Congo Bongo, released in February 1983. Another early isometric platformer, the ZX Spectrum game Ant Attack, was later released in November 1983.
Knight Lore, an isometric sequel to Sabre Wulf, helped to establish the conventions of early isometric platformers. This formula was repeated in later games like Head Over Heels and Monster Max. These games were generally heavily focused on exploring indoor environments, usually a series of small rooms connected by doors, and have distinct adventure and puzzle elements. Japanese developers blended this gameplay style with that of Japanese action-adventure games like The Legend of Zelda to create games like Land Stalker and Light Crusader. This influence later traveled to Europe with Adeline Software’s sprawling epic Little Big Adventure, which blended RPG, adventure, and isometric platforming elements.
Before consoles were able to display true polygonal 3D graphics, the ¾ isometric perspective was used to move some popular 2D platformers into three-dimensional gameplay. Spot Goes To Hollywood was a sequel to the popular Cool Spot, and Sonic 3D Blast was Sonic’s outing into the isometric subgenre.

Reference: Wikipedia