Greg Tiernan (born on 19 June 1965 in Dublin, Ireland) is an Irish-born Canadian animator, director, producer and voice actor. He is the Chief Creative Officer and co-founder of Nitrogen Studios. He was the director of Thomas & Friends from 2008 to 2012. He began work directing the series after the CGI transition, taking over from Stephen Asquith.
He was born in Ireland and started Nitrogen Studios in 2003 with Nicole Stinn.
Other work includes, "The Land Before Time", "An American Tail", "All Dogs Go To Heaven", "Happily N'Ever After", "Trollhunters", "Sausage Party" and "The Addams Family".
- "Sausage Party" (2016)
- "City in Crisis" (2015)
- He is married to Nicole Stinn.
- He has been working in the animation industry for twenty-seven years.
- Tiernan is a super fan of the Railway Series who owns a copy of both The Island of Sodor: Its People, History and Railways and Sodor: Reading Between the Lines.
- In an interview with SiF, Tiernan expressed a desire to remake Pop Goes the Diesel and Dirty Work. If it was his choice, he would bring back every character ever introduced.
- In an interview on 98.3 Vancouver, Tiernan told the hosts of the radio station the reason why Nitrogen stopped working on Thomas was that they only wanted their team to focus one single project, along with saying they thought it was best to finish their career on the show.