Here it is, the one that started it all, the grandaddy of all mechs, Gundam RX-78-2 by nobu_tary. There may have been other giant robots before, but this is the one that turned mecha anime into a thing. Originally airing in 1979 this guy is probably older than many of you reading this post (but not me, man I'm old) but I'm guessing you've seen him before. That's staying power, and a testament to his pedigree.

Gundam RX-78-2