Tektronix XP29P
The Tektronix XP29P was the first PEX terminal from Tektronix introduced in May, 1991 at a base price of $6,995. PEX, the PHIGS Extensions for the X Window System, brought 3D graphics to the X Window System.
References
"Tektronix Offers First X Window PEX Terminal for 3-D Graphics Transmission", InfoWorld, May 6, 1991, pg. 33