Olha Petrivna Kosach, better known by her pen name Olena Pchilka, was a Ukrainian publisher, writer, ethnographer, interpreter, and civil activist. She was the sister of Mykhailo Drahomanov and the mother of Lesya Ukrainka, Olha Kosach-Kryvyniuk, Mykhailo Kosach, Oksana Kosach-Shymanovska, Mykola Kosach, Izydora Kosach-Borysova and Yuriy Kosach.