Legendary anime? Though there are lots to be named as legendary like some of the shows already mentioned my pick is a toss up between three classics: Doraemon, Mazinger Z, and Astro Boy.
Doraemon is one force to be reckoned with...its light hearted tv show runs since '79 up to this very day and the manga ran for 20 years. Doraemon is one of the most recognized characters of Japan along with Astro Boy, Mazinger Z, Godzilla, Ultraman, Hello Kitty, and a few others. My aunt who studied college in Japan a long time ago even told me that they read and used Doraemon for some fancy schmancy literary subjects at school...Doraemon is downright iconic, and you don't have to be in Japan to realize that...
Mazinger Z is one of the earliest mecha and super robot shows, it is responsible(along with Tetsujin 28) for the mecha boom that spanned 2 decades. Its legacy is evident even to this day, its influence is seen in almost all mecha shows. The massive success of its merchandise such as toys and video games proves that Mazinger Z is far from being a buried memory.
In my opinion nobody embodies anime better than Astro Boy. It is a Tezuka masterpiece and the east's answer to the Mickey Mouse of the west. Like the ones i've mentioned, his legacy lives up to this day...through what we know now as anime.
Up to now, i don't know if there is a show that could match up to the sheer artistic, commercial, and influential success of these three...crushing competition for decades.
