Mangaka
Mangaka (漫画家, Mangaka? lit. 'comic artist') is the Japanese word designated to refer to the creator of a comic strip or comic. Outside of Japan, mainly in the West, the word is used to refer to manga authors. The word is made up of the noun manga, which means 'comic', and the suffix -ka, which is an aggregate meaning 'creator of', giving the word an honorific degree indicating mastery. The mangaka of a title only captures it in manga.
Some artists study for a few years at an art school, or learn from other mangakas as assistants, before starting their career as a professional. Takeuchi won a Kodansha-sponsored contest, Osamu Tezuka worked without having been an assistant, and also Masashi Kishimoto.
A mangaka's work usually encompasses the majority copy of the final or middle work of a Western comic, both plot and story art, although it's rare to find a mangaka doing art based on an original story given by a writer or who receives help in drawing details, such as landscapes, coloring or even character design. There are even cases where several mangaka work as a group to develop a final product, as is the case of the CLAMP group, although it is less frequent.
Collaborators
Editor
Many professional mangaka work with an editor, who is considered the mangaka's boss and the project's production supervisor. The publisher offers advice on the manga art, story, continuity, generally looking for the manga to meet the standards of the company or publisher. This is the case of Akira Toriyama and his former editor Kazuhiko Torishima, who also worked as a publicist for the series produced; Among other tasks, the editor can supervise the designs, the merchandise of the product, adaptations to animation, among others.
Writer
A mangaka can both write and illustrate a series of their own creation, or work in collaboration with another author. In cases where the writer and illustrator is someone different, both must maintain fidelity both in the dialogue and in the drawing. Cases like Takeshi Obata from Death Note or Aki Shirou and Hajime Kamoshida from Sakura-sō no Pet na Kanojo are examples of manga artists who have worked with writers for almost their entire career.
Wizards
Many mangaka have assistants who help them with their work. The functions of the assistants can be very varied, some mangakas only deal with the basic parts of the manga, having many assistants that carry out the details, while others only leave specific tasks to their assistants (Gō Nagai, for example, uses a wizard specifically for drawing helicopters and other military vehicles). Other mangaka don't have assistants, preferring to do everything themselves, although to meet tight deadlines assistants are often necessary.
Most of the time, the assistants are responsible for the backgrounds of the manga, while the mangaka draws the main characters. Although they are often employed to help with the art, the assistants almost never help the mangaka with the plot. Most mangaka started out as an assistant, for example, Miwa Ueda assisting Naoko Takeuchi, Leiji Matsumoto assisting Osamu Tezuka, Kaoru Shintani assisting Leiji Matsumoto, and many others. However, it is also possible for an assistant to carry out his entire career as such, without becoming a mangaka.