The drawings, for what is now Triplex Italic, were done in Iowa City in 1985 by John Downer. The italic was originally conceived as a companion for another typeface being drawn at the same time called Arcatext, which (like Triplex) could be described as a "humanist sans-serif" having simplified character shapes constructed mostly of geometric parts.
At one stage, a certain customer was interested in Arcatext but wanted a different italic drawn for it, so the plan for the italic took another direction and the idea for this one was dropped. Five years later, Emigre decided to commission the abandoned italic as a digital typeface in three weights as companions to the Triplex Sans and Serif families designed by Zuzana Licko in early 1990.
The ascenders and descenders have been shortened to match those of Triplex and the new capitals embody more of the features that distinguish the lower case, but otherwise the digital version closely follows the original drawings.
Triplex Italic Main Page