An electro-mechanical machine used by the United States Golf Association to test golf clubs and golf balls for conformity to standards. Copies of the robot are used by individual manufacturers such as True-Temper and Wilson Sports.

That's the dry answer. Iron Byron is actually a robot named after the great Byron Nelson, whose swing was so consistent and perfect that legend has it that only a mechanical man could replicate it.

Iron Byron can be adjusted to repeat the same swing ten thousand times which is useful for comparing the relative properties of clubs and balls. If such-and-such a new model of golf ball is submitted by a manufacturer for approval by the USGA, it gets smacked a few hundred times by the machine and the average distance the ball travels forms the basis of whether it conforms to acceptable limits of carry and roll for a given swing velocity.

Iron Byron's swing is so consistent that the USGA claims it must replace the center line of the test fairway every two years because of the turf damage caused by golf balls landing in the same spot over and over and over again, between 1000 and 2000 times per day during the summer months.

Other factoids as reported by The USGA in their Golf Journal:

The driver used to test golf balls snaps roughly every 9000 swings. By the way, that driver is a Spalding laminated wood driver with metal shaft of "extra stiff" flex.

Iron Byron has made 7 holes in one.

You can visit the original model which is on display at the USGA Museum.

Year 2000 Update: The USGA is switching their method of testing ball compliance from outdoor to indoor and will no longer use Iron Byron to propel each ball down range. The robot is being retired!

Iron Byron is not an anthropod, meaning that it's not shaped like a human being. It doesn't walk. It doesn't talk. If fact, it has more in common with one of those automated welding machines you'd see on an automobile assembly line than it does with anything you'd see in a science fiction movie. It's basically a floor-mounted pedestal, maybe 4 or 5 feet tall, atop which is mounted a swiveling machined-metal arm, articulated with elbow and wrist hinges to mimmick the dimensions and motion of a human swing. An adjustable sleeve at the end of this hinged arm is used to fasten the club being used during tests.