Is Atari a game developer or game publisher?

Hello! I am just curious as I am getting hooked to Atari 5200 games. I downloaded a bunch of roms and somehow I am amazed. Anyway, is Atari a game developer or game publisher, because roms' file names like the

Code:

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Berzerk (1983) (Atari)

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I can't say if they are the one who developed it or they published it.

Also, what is Prototype? Is it something like "Alpha/Beta" Version, or its a game developer? or publisher?
Because some roms have file name like:

Code:

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Black Belt (1982) (Atari) (Prototype)

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Code:

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Plutos (Tynesoft) (Prototype-NTSC)

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Thank you

Atari used to be both, then they went out of business. The current Atari, I believe, is just some company that bought the name and is farming out games to other devs to cash in on name recognition.