Southern Whites (which really equals Don Cossacks + anti Bolshevik officers and generals fleeing south):
Kaledin, Krasnov = Occupied the position of leader of the Don Cossacks (ataman
) in succesion. Kaledin died before June 1918, so you won't see him in the Grand Campaign scenario.
Kornilov = White General. A very strong-minded and bold person (think Patton without all the military successes). Attempted a coup d'etat against Kerensky, was imprisoned, escaped south. Dies early in 1918, so you won't see him in the Grand Campaign scenario.
Denikhin = White General. Pretty much the person in charge of the whole Russian war effort in the South after Kornilov's death.
Alekseyev = Prior to the revolution, Chief of Staff and then Commander of the (whole) Russian Army.
Wrangel = commander of the White Army in the South in its last phases.
(I think I'm forgetting somebody...)
Yudenich = Commander of White Russian troops to the west of Moscow, i.e. Baltic States. Attacked Petrograd at some point. I don't know much more, I'm sure others do.
Kolchak = Admiral. Gained renown in the Baltic Sea and in the Black Sea during WW1. Takes control of Siberia in late 1918 (one of the scenarios starts exactly at that moment).
The Czech Legion (yes, they are a major figure
) : Czech soldiers who had fought for the Austro-Hungarian empire (since their lands were part of it) and who during the war were imprisoned and persuaded to fight on the side of Russia. When the revolution(s) happened they were left pretty much to fend for themselves. Caused *major* headaches for the Bolsheviks in Siberia.