On the Fahrenheit scale, the freezing point of water is 32 degrees and the boiling point is 212 degrees. Zero Fahrenheit was the coldest temperature that the German-born scientist Gabriel Daniel Fahrenheit could create with a mixture of ice and ordinary salt. He invented the mercury thermometer and introduced it and his scale in 1714 in Holland, where he lived most of his life.

Supposedly 100 degrees Fahrenheit is the approximate rectal temperature of a healthy cow, according to Grzcyrgba, but I think that's just serendipity.

Fahrenheit originally wanted the scale to be as 0 the coldest temperature he could get, and 100 degrees as the temperature of a healthy human. His calculations were off, maybe because the temperature in your mouth and ears and armpits and rectum is a few degrees off from your core temperature, and the average temperature of a human is actually at 98.6 degrees.