Wiktionary
n. (context manga English) A professional manga or anime artist.
Wikipedia
is the Japanese word for a cartoonist. Outside Japan manga usually refers to a Japanese comic book and mangaka refers to the author of the manga, who is usually Japanese. As of 2006, about 3000 professional mangaka were working in Japan.
Most mangaka study at an art college or manga school, or take on an apprenticeship with another artist before entering the industry as a primary creator. More rarely a mangaka breaks into the industry directly, without previously being an assistant. For example, Naoko Takeuchi, author of Sailor Moon, won a contest sponsored by Kodansha, and manga pioneer Osamu Tezuka was first published while studying an unrelated degree, without ever working as an assistant.
A mangaka will rise to prominence through recognition of their ability when they spark the interest of institutions, individuals or a demographic of manga consumers. For example, there are contests which prospective mangaka may enter, sponsored by manga editors and publishers. They are also recognized for the number of manga they run at one time.