What was the first ever manga?

The man generally credited as being the first manga artist is Osamu Tezuka. There had been other manga-like woodblock carvings before that point as well, but Tezuka's 'New Treasure Island' (an adaptation of the novel, 'Treasure Island') became the first manga and was an instant hit. You are more likely to recognize Tezuka for his later manga, 'Astro Boy'.

Manga was created between the 1950's and 1960's.