I’m not sure if anyone has suggested this before or asked a similar question, but I’ve had a look at this list of Heroes in AoE II:
and there are quite a few historical characters which don’t appear in any Campaign or Historical Battle:
Hrolf the Ganger (Vikings)
The Black Prince (Britons)
Alexander Nevski (Slavs)
Frederick Barbarossa (Teutons)
Abraha Elephant (Ethiopians)
Guglielmo Embriaco (Italians)
Huayna Capac (Inca)
Miklos Toldi (Magyars)
Mustafa Pasha (Turks)
Pacal II (Mayans)
Richard de Clare (Franks/Britons)
Su Dingfang (Chinese)
Zawisza the Black (Slavs/Lithuanians; appears in Kurikara, but not civ-specific)
Jayanegara (Malay - NPC in Gajah Mada)
Wang Tong (Chinese)
Henry the Lion (Teutons - NPC twice in Barbarossa)
King Bela IV (Magyars - NPC twice in Kotyan Khan)
Leif Erikson (Vikings)
Vasco da Gama (Portuguese)
Vytautas the Great (Lithuanians; appears in Cyprus, but not civ-specific)
Cuauhtemoc, Saladian & Frederick Barbarossa all have their specific campaigns (Cuauhtemoc in Montezuma) but don’t appear ingame, as well as Henry the Lion who even has dialogue in the missions that he appears in the Barbarossa campaign.
I’ve only seen one suggestion for Asian Campaigns, one of which includes the hero Su Dingfang, but there are plenty of others from the remaining heroes.
My possible suggestions:
Alexandr Nevski - Battle of the Ice: April 5, 1242
Zawisza Czarny - Battle of Grunwald: July 15, 1410, Hussite Wars, Siege of Golubac
Vytautas the Great - Battle of Grunwald: July 15, 1410
Slavs and Lithuanians are missing their own unique campaigns, so maybe having a Battle of Grunwald would be a great addition!
If anyone else has any other ideas for battles featuring these Heroes, or how to add relevant ones to the existing campaigns, please post here!