Why would a grown man want to dye his beard green on St. Patrick's Day?

Some will argue that THIS very day should be a holiday! Alas, it's not. And if it falls on a workday, you must go to work. But there is no rule that you can't have fun! Ha! I am sporting a green beard... and a green bandana! I am so cool.

Well, it looks like some of my coworkers recieved the memo!

 

So, who is this St. Patrick guy?