Unlike DirectX, OpenGL isn't much of a changing standard. It does in fact come with the video card drivers.
Older hardware, for instance the original Voodoo2 or the Matrox G200 needed an "OpenGL Wrapper" to run OpenGL. Basically, this was software that translated OpenGL calls into some other native graphics API. In the case of the Voodoo2, OpenGL calls were translated to GLide calls, which was just 3dfx's own version of OpenGL.
OpenGL itself was originally created by Silicon Graphics, if I remember correctly.
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