Euclid was a Greek mathematician who laid the foundation stones for the formal study of geometry. He proposed a series of "self-evident" postulates governing how points and lines and angles and stuff behave, and from there derived a lot of the geometrical theorems we still rely on today.

Kebabs are Greek or Turkish food items made by rolling hot sliced meat and salad items in pita bread. I'm not sure if they had been invented in Euclid's time, but anachronism is the least of this comic's concerns. (Technically this is döner kebabs; there's also shish kebabs, where the meat is strung on a skewer, but most people talking about "kebabs" mean döner kebabs.)