RDP is based on Citrix ICA which builds on Citrix Multiuser released in 1991 for OS/2, and 1992 for DOS, 1993 for Windows.

https://www.basvankaam.com/2017/03/29/a-lesson-in-history-th...

The Citrix/Microsoft relationship is a bonkers story. The world didn't yet know that licensing your tech to Microsoft meant you were going to grab your ankles.