Baba Agnieszka is one of eight living warlocks who claim to have been born earlier than Jonathan Shadowhunter. She is said to be the elder sister of Elphas the Unsteady. She has lived quietly in Idris since 1452, in a cottage built and maintained for her by the Nephilim in honor of her family connection. Agnieszka appears to have deteriorated mentally due to a slow decay caused by eccentricity and isolation. She is something of a relic, but to the Nephilim, she is a holy relic.
The term has come to be used in many languages as a term for various family members. It means grandmother in many Slavic and Serbo-Croatian languages. Baba is transparently a babble word, meaning "woman", or, specifically, "old woman". In modern Russian, the word бабушка babushka ("grandmother") derives from it, as does the word babcia (also "grandmother") in Polish or бабця babcya in Ukrainian.
Baba may also have a pejorative connotation in modern Ukrainian and Russian, both for women as well as for "an unmanly, timid, or characterless man". In Polish, the term is considered to be pejorative, meaning 'vicious or ugly woman'. In Czech, both of those meanings apply. It is also a Persian honorific term used as a mark of respect to refer to Sufi saints, and for fathers, wise or old men in Shona, Yoruba, Greek, Hindi, and many other languages.