It all starts in 1978 when the Japanese company Toei signs an agreement with Marvel to license each others' characters over a three-year period, during which time a Japanese Spider-Man series was produced. The results were interesting.
That's right, Spider-Man has a giant robot, which I guess is why in the show he introduces himself as the messenger from hell. 'Nuff said.
Toei took this idea of the mecha-accessory and ran with it, introducing it into their long-running Super Sentai franchises. These were a genre of shows about a small team of color coordinated fighters (the term 'Sentai' was applied to squads in WWII) who would battle a variety of alien and/or magical threats using special powers and lots of kung-fu. Dozens of these shows were produced, and a few continue to this day.
After the webslinger introduced the giant robot concept (given to him by the alien Garia), other Sentai shows began toying with the idea, including one called Kyōryū Sentai Zyuranger. In 1993, U.S. studio Saban Entertainment shot new scenes with American actors, edited it together with licensed and redubbed action footage from Zyuranger, and brought the show to American audiences as Power Rangers.
So the next time you see the Megazord defeat one of Rita Repulsa's gargantuan goons, give a salute to the wall-crawler who does whatever a spider can, including summon a giant robot.