Yes I know Tanya/Red Alert is from 1996, but I'm asking about before that.
To be clear, I'm interested in characters (units) in western real time strategy games which have unique capabilities and of which only 1 copy can be built/acquired during normal campaign games.
Were there any such characters? Were they gung-ho commando-style units like Tanya, or were they very different?
Warcraft by Blizzard came out in 1994, and had hero units. These heroes had unique combat stats and vital to the campaigns, but really weren't great warriors. Spellcasting was limited to regular caster units, the heroees had no special ability (that I can recall).
Before Warcraft there were a few console games which had RTS elements, but I don't think we'd recognize them as an RTS. What we'd recognize as an RTS would be the aforementioned Command and Conquer series, and Dune. Dune didn't have unique or hero units. (It DID have pretty awesome sonic tanks and sandworms which would eat your reapers, though.)
The original Command and Conquer offered a "commando" unit, IIRC, that was unique and had Tanya-like features.