Merlin the Wizard, or just 'Merlin', is a wizard in the King Arthur tale/legend, if you've heard of it. (A lot of people had.)
Merlin helped King Arthur do stuff, I think, and if you know the legend, you should know King Arthur pulled the sword Excalibur from a stone. The legend has been around for a long time.

I honestly don't know that much about the legend, just that Merlin helped Arthur, and of course the Excaliber sword, stone, etc. I'm not sure if this was how he looked, but when I think Merlin Wizard, a person with a gray beard and a blue cloak with white-star things on it is what I think.