Thomas Douglas Selkirk Duff (born December 8, 1952) is a Canadian computer programmer.

Duff was born in Toronto, Ontario, Canada, and was named for his putative ancestor, the fifth Earl of Selkirk.

Duff worked at the New York Institute of Technology Computer Graphics Lab and the Mark Williams Company in Chicago before moving to Lucasfilm's Computer Research and Development Division.

Duff later worked for 12 years at Bell Labs Computing Science Research Center, where he worked on computer graphics, wireless networking, and Plan 9;[3] in the course of his work there, he authored the well known "rc" shell for the Version 10 Unix operating system.

Duff worked at Pixar Animation Studios from 1996 until his retirement in 2021.