Liam O'Brien is an American voice actor, voice director, and writer known for his extensive work in English-language adaptations of Japanese anime, as well as for his prolific contributions to animation and video games. Born Liam Christopher O'Brien on May 28, 1976, in Weehawken, New Jersey, he developed an interest in acting during high school and later attended the New York University Tisch School of the Arts. He began his career in theater before transitioning to voice-over work in New York City, a move facilitated by fellow actor Crispin Freeman. He is married to voice actress Amy Kincaid.

O'Brien has built a reputation for taking on a wide variety of roles, often portraying characters with a dark, insane, or villainous edge, as well as those considered to be "evil geniuses". This has become a recurring theme in his casting. Some of his most iconic and enduring roles include Gaara in the Naruto series, Captain Jushiro Ukitake in Bleach, and Lloyd Asplund in the Code Geass franchise. His filmography is vast, encompassing many of the roles listed in the query, such as Yuri Petrov, also known as Lunatic, in Tiger & Bunny 2; Dan Moroboshi in Ultraman; Gihren Zabi in Mobile Suit Gundam: The Origin: Advent of the Red Comet; and Tokugawa Ieyasu in Sengoku Basara - Samurai Kings: The Last Party. He also voiced Dr. Clive in the Haré+Guu series and its sequel, Frisbee in the film Redline, Genpou Saji in Ikki Tousen: Great Guardians, Bud Mint in K.O. Beast, Hideaki Asaba in His and Her Circumstances, Hisoka Kurosaki in Descendants of Darkness, Dizelmine in Lagrange - The Flower of Rin-ne, Raiko in Legend of the Millennium Dragon, and the villain Red Skull in both Marvel Future Avengers and Marvel Disk Wars: The Avengers.

In addition to acting, O'Brien is a highly accomplished ADR writer and voice director. He has written English adaptations for series like Naruto and has directed voice-over work for hundreds of episodes of anime, as well as for major video game titles such as The Last of Us, Resident Evil 5, and Resident Evil 6. His voice is also instantly recognizable to gamers for roles like War in Darksiders, Asura in Asura's Wrath, Caius Ballad in the Final Fantasy XIII series, Yasuo in League of Legends, and Illidan Stormrage in the Warcraft franchise.

Beyond traditional voice-over, O'Brien is a core cast member of the popular web series Critical Role, where he and other voice actors play Dungeons & Dragons. He also co-hosts the podcast All Work No Play with fellow voice actor Sam Riegel. His talent has been recognized with awards, including the BTVA Anime Dub Award for Best Vocal Performance in an Anime Movie/Special in a Supporting Role.