You probably know it as: Soap
Ok, so it's actually an oversimplification to call this one compound "soap", but this long chain molecule is an ingredient you'll probably find in just about every cleaning product you own. Soap, from a chemical perspective, is the product of a saponification reaction - a reaction between fat and a strong base (usually sodium hydroxide). The soap making scenes in Fight Club, including the chemical burn, are surprisingly accurate for movie science (though I wouldn't exactly recommend working with their starting materials).
SLS is used as an engine degreaser, shampoo, floor cleaner, a moderately effective shark repellent, and car wash soap. Believe it or not, it's also found in your toothpaste. You may not realize it, but your toothpaste is basically just a tastier, thicker version of your shampoo (I'll bet you didn't realize you were brushing your teeth with shampoo, did you). SLS is also the reason that orange juice tastes so horrible after you've brushed your teeth (probably because of it's surfactant properties).
So the same chemical that is used as an engine degreaser can be used as a shark repellent and is also found in your toothpaste. You'll often hear the argument that chemical X is bad for you because it is also used in product Y, but a chemical isn't bad because it's also found in a different product, even if that product would be bad for you. As another example, polysorbate 60 is used in many processed foods as well as in sexual lubricants. It's an easy argument to say you shouldn't eat foods that contain polysorbate 60 because you're basically eating KY Jelly, but it's not a good argument. Chemicals can have a wide variety of applications - your toothpaste is proof of that.