Gregory Tiernan (born June 19, 1965) is an Irish-born, Canadian-based animator, director and voice artist. Along with his wife Nicole Stinn, he founded Nitrogen Studios Canada, Inc. in 2003, through which he introduced CGI to the Thomas & Friends series. Prior to this, Tiernan collaborated on various projects with filmmaker Don Bluth, Walt Disney Animation Studios and Klasky Csupo, Inc. Tiernan made his feature film debut with the long-gestating R-rated animated film Sausage Party (2016), joining Conrad Vernon to direct production of a story conceived by Seth Rogen, Evan Goldberg and Jonah Hill.