Mercedes is a luxury sports car company located in Germany and founded in 1900. Karl Benz was the inventor of the first gasoline-powered automobile, the 1886 Benz Patent Motorwagen. The name Mercedes-Benz first appeared in 1926.
AMG models typically have a more aggressive appearance, higher level of performance, better handling and stability, and more extensive use of lightweight body materials than their regular Mercedes counterparts. They typically don't stip out driver luxuries in order to reduce weight, so they are still bought as daily driver vehicles.
Another step up from the base Mercedes models, the top-of-the-line AMG models are designated "AMG Black" and built in limited numbers. These models take the performance modifications a step further, but still retain the level of luxury Mercedes expects from its vehicles. (They are not "race cars for the road" that some companies produce with their tuning.)