1) Origin: Constantine, Costas
From the latin word ''constant'' which means steadfast. But another meaning of constant is ''obedient, loyal'', so Kostas could mean ''loyal friend'', an awesome, good friend.
2) A name used a lot by Greeks. It's also a Christianic name.
1) ''You have to meet Kostas, he's such a loyal friend, I'm telling you; he's as close as his name!''
2) Kostas is so popular in Greece, especially because it's a Christianic name, because of the GrecoRoman King Constantine, who happens to be a saint.