U.S. Patent # 3,285,228 is the AG7 anti-gravity pen designed by Paul Fisher, who founded the Fisher Space Pen Company. Not surprisingly, the AG7 is the same space pen.
An old urban legend holds that NASA spent a million dollars developing a pen that could be taken into space and would still function in zero gravity, only to find out that the Russians thought to use a pencil. Not true. Actually, NASA still uses pencils, or at least grease pencils. Regular pencils have the problem of being a bit too flammable.
Paul Fisher set out to develop a pen that could be sent up in space in the 60s. He had already made a name for himself by developing a universal refill cartridge- before this, there were several different types of refills that were not interchangeable between different types of pens, but his could be used with most of them.
He then set to work developing the space pen, had it patented by 1965 and gave it to NASA for testing. They first used the pen on the Apollo 7 mission in 1968. The space pen can write upside down, under water, and in extreme temperatures.
The pen uses a thixotropic ink: meaning the ink is a gel that is viscous until somehow shaken or stressed, as by the roller ball, in which case it liquefies. Fisher developed a thixotropic ink earlier for the Fisher universal ink cartridge. This allows the ink to flow only when needed.
Furthermore, the cartridge is pressurized by nitrogen, which is why it doesn't need gravity to work.
Fisher died in 2002, but they still make the pens. The factory store is located in Boulder City, Nevada.