here's abc's darren rovell. >> reporter: he's the fighting spirit of ireland. >> conor mcgregor! >> reporter: 27-year-old conor mcgregor is the next star in professional mixed martial arts. the sport looking for the next big thing after ronda rousey's shocking defeat. mcgregor is looking to make history this weekend by becoming the first irish champion in the ufc. >> before me, nobody knew nothing about this sport. i'm proud to be putting my nation at the forefront of the fight game where we belong. >> reporter: the mighty irishman, reminiscent to some of the brash boxer mickey from the movie "snatch." the tattooed mcgregor commands attention with bold moves in the octagon. his cocky assuredness and his mouth. feet on the desk, not one of about it. >> reporter: drawing comparisons to a young mohammad ali. he lives big too. mega mansions, custom suits, big cars. >> my name is conor mcgregor. >> reporter: when his first job as an apprentice plumber in ireland didn't work out he turned his focus to boxing with a dream of making it big. >> my dream is to be world champion in the ufc.

here's abc's darren rovell. >> reporter: he's the fighting spirit of ireland. >> conor mcgregor! >> reporter: 27-year-old conor mcgregor is the next star in professional mixed martial arts. the sport looking for the next big thing after ronda rousey's shocking defeat. mcgregor is looking to make history this weekend by becoming the first irish champion in the ufc. >> before me, nobody knew nothing about this sport. i'm proud to be putting my nation at the forefront of the

. >> reporter: for "nightline," i'm darren rovell in new york. >> and just how confident is mcgregor that he's got this? anyone who bets he wins with a knockout in round one is invited to his after party for free. everybody wins. thank you for watching abc news. tune into "good morning america" tomorrow. and as always, we are online 24/7 on our "nightline" facebook page at abcnews.com. good night, america. tom: now at 10:00, an army ranger from new hampshire has been killed in a training exercise. describing just how special her brother was.

. >> reporter: for "nightline," i'm darren rovell in new york. >> and just how confident is mcgregor that he's got this? anyone who bets he wins with a knockout in round one is invited to his after party for free. everybody wins. thank you for watching abc news. tune into "good morning america" tomorrow. and as always, we are online 24/7 on our "nightline" facebook page phil! oh no... (under his breath) hey man! hey peter. (unenthusiastic) joanne? is that you? it's me... you don't look a day over 70. am i right? jingle jingle. if you're peter pan, you stay young forever. it's what you do. if you want to save fifteen percent or more on car insurance, you switch to geico. you make me feel so young... it's what you do. you make me feel so spring has sprung. i just want the most wonderful holiday ever. you should get holiday scratch-offs from the new york lottery. you can talk? come on, brian. there's more chances to win than ever. with a sweepstakes to win $500 a week for life. (wife) who are you talking to? nobody! new holiday scratch-off games >>> two people shot in brooklyn. a very a