Similar to how Spore handled what types of Empires you found in the Space stage, I think Thrive should handle that similarly.
Biologists - Biologists seek knowledge and wish to learn more. Life exists to be understood and studied.
Conquerors - Conquerors take what they want with force. They wage wars on others who oppose them. They enslave the weak for their own personal gain.
Warriors - Warriors are among the brave and the bold. Armed with spears and heavy artillery, stylized with trophies of the enemy, they stand amongst their allies.
Politicians - Basically just Diplomatics in Spore
Merchants - Merchants travel the galaxy, trading with the rich to get the big bucks. Allying with a merchant might win you the lottery!
Shamans - The same thing as in Spore
I tried to add a humorous tone to these descriptions, to have that old spore feel