Steadfast

Steadfast was the mount of the legendary Uther the Lightbringer.

Speculation
In the Warcraft III mission Digging up the Dead, five riderless horses can be seen in a pen near Uther in Andorhal. One of these horses may have been Steadfast. If so, the horse likely followed his master into death shortly after Uther was killed by Arthas Menethil.