As already mentioned, a POT-like device with enough current capacity would typically be called a rheostat.
The best mating of fans to any controller is to use fans with a max (@ 12V) RPM spec that is just a little more than you might ever need, not a 5K RPM fan you will always run at less than 1/2 speed (which is what I expect, 2500 RPM is still a little audible and a reason to move up to a larger fan or heatsink if a nearly inaudible system is the goal). The reason for this is that below a certain threshold the fan motor torque causes a pulsation, you can actually run one at a slowest absolute value if picking the slower spec'd part in same fan family. Ideally you want the resultant controlled speed of the fan to be as high a % of the original speed as possible, to arrive at any particular RPM result. It just takes some experience or trial and error if you have a new type of case or parts to see how temps respond to fan speed changes.
Generally with the fan you have proposed you'd need a resistance around 68Ohm (+- a few dozen ohm). With a slower default speed fan, particularly those very large fans which hardly need to spin at all to move enough air in an underclocked PC, you might need rheostat values up to about 150Ohm. Thus for best control you want to select a rheostat valuejust above your desired upper value.
The thing about rheostats is that while they're easy to implement, they also get quite expensive. Like with power resistors you don't really want to run one at it's max wattage rather derating it so it doesn't run hot. Last thing you want is to add complications, significant failure points to a vital cooling subsystem in a computer, it should stay as reliable as reasonably possible.
For best fan control you do not want a switching or linear voltage regulator unless you are only using very cheap fans which have terrible motor torque, undersized magnet. By "best" I reallymean smooth operation at low RPM, not best range of adjustments on most of the RPM range till you get to a lower thrshold, which can be a wash depending on exactly what is compared and contrasted among the different methods of control.
Otherwise the slower the fan turns, the more the fan starts to stall and lurch faster again (X times a revolution, 4 with some) with only a voltage control, making it even louder that it could have been but with lower airflow too. To keep the fan turning smoother at low speed the result is better with current control (limitation). A rheostat will do this, or a simple series resistor, or even an LM317 in current, not voltage, regulation mode.
Personally I don't want or need knobs sticking out on a PC so I often use one rheostat rigged with a couple fan adapters (4 pin molex socket and 3 pin mini 0.1" types) to dial-in the resistance any particular fan-PC-environment combination will need, then having that value a cheap and unobtrusive 1-2W resistor can be chosen for permanent installation instead of the rheostat.