Song Joong-ki as Vincenzo Cassano / Park Joo-hyung
An Italian lawyer and Mafia consigliere of Korean descent. He is the adopted son of the late boss of the Cassano Family.
Jeon Yeo-been as Hong Cha-Young
A lawyer who is an associate for the Wusang Law Firm and the daughter of Hong Yoo-chan. Energetic, she tends to overreact. She later replaces her father as CEO of Jipuragi Law Firm. She joins Vincenzo in his vendetta against Babel Group.
Ok Taec-yeon as Jang Jun-woo / Jang Han-seok.An intern in Wusang Law Firm working under lawyer Hong Cha-Young as her personal paralegal/assistant, and the true CEO of Babel Group. He puts on a front as a happy-go-lucky, dumb, and naive man.
Kwak Dong-yeon as Jang Han-seo
The half-brother of Jang Jun-woo and the previous Chairman's illegitimate son who publicly acts as Chairman of Babel Group in his brother's place. He appears rude, cocky and pretentious. He doesn't have book smarts but has enough street smarts to take sides with Vincenzo against his brother.
Kim Yeo-jin as Choi Myung-hee
A former prosecutor who quits the prosecutor’s office to join Wusang Law Firm as its new Senior Partner, and in the process becomes the corporate fixer and attorney to the Babel Group. She appears good-natured and enjoys Zumba dancing but is, in reality, extremely corrupt.
