The SI unit for temperature is kelvin (K) named after the physicist William Thomson, 1st Baron Kelvin, who proposed it in 1848. The kelvin scale starts at 0 K as a reference point in classical thermodynamics where all thermal motion ceases. Each unit of kelvin is defined as 1/273.16 of the thermodynamic triple point of water (0.01 °C or 32.018 °F).
The Celsius scale was created in 1742 by Anders Celcius with 0° defined as the boiling point and 100° as the freezing point of water. The scale was reversed to the current definition of 0 °C for the freezing point and 100 °C for water in 1744. Most countries today use the Celsius scale with exception of the Bahamas, Belize, the Cayman Islands, Palau and the United States who use the Fahrenheit scale.
Daniel Gabriel Fahrenheit proposed his scale in 1724 and originally defined 0° as the lowest temperature at which he could muster brine (salt solution). Today the scale is defined by marking 32 °F as the freezing point of water and 212 °F as the boiling point.
René Antoine Ferchault de Réaumur was a French scientist contributing to many of the fields of natural sciences amongst creating the scale which bears his name.
The Rankine scale was proposed by physicist William John Macquorn Rankine in 1859. It is similar to the Kelvin scale whereas 0 °R; equals the absolute zero