Tex is a robot character. Although he did not appear in a Pixar feature or short film, he was created by John Lasseter for the THX sound system that used their sound system for Pixar films 1995-2007. He appeared in three THX trailers. The first was released in 1997, the second in 2001, and the third in 2006.
Tex flying around the THX logo in the first trailer
Tex in front of the THX logo in the first trailer
Tex with a moo can in front of the THX logo in the second trailer