Koirala () is a predominantly Brahmin(Bahun) as well as Khatri Chhetrisurname of Nepal,All koirala share the same gotra, Moudgalya,which means all of them share the same forefather, so a koirala can't marriage with another koirala.
It can refer to:
Moudgalya also known as Mudgal, a ancient Monk, common forefather of all koiralas
Manu Koirala Served as Prime minister of Sen thakuri kings of Udayapur(Chaudandi, Bijayapur)
Damoder Koirala Served as commender in Chief as well as Prime minister of Sen thakuri kings of Makawanpur
probabely only brahmin, who serve as a army chief in nepalese histry