Colin Farrell -- Conor McGregor Could Be King (VIDEO)

Conor McGregor is the greatest thing to come out of Ireland since Guinness -- or at least that's how you're gonna feel after watching his countryman Colin Farrell gush about the UFC badass.

We got Colin outside Jimmy Kimmel's studio Thursday evening ... and, somewhat foolishly, asked if he was a fan of the UFC Featherweight champ. Colin went way beyond Conor's fight skills, and went off about his character and spirit.

He even says Conor's having a HUGE effect on "all the people at home." Check it out ... Colin makes it sound like Conor could be a bona fide Irish leader. Take that Bono!