While attending university in Zurich, Einstein fell in love with an older physics student, Mileva Marić, who would eventually become his first wife. By the standards of late 19th-century Europe, theirs was a modern love affair. They soon grew quite close and gave one another nicknames: He called her "Dollie," and she nicknamed him "Johnnie."
Marić was a remarkable woman, having overcome enormous social resistance to earn a place as the fifth woman accepted to the prestigious university [sources: PBS]. But for years after graduation, Einstein remained too poor to marry her. Moreover, his parents rejected Marić as a too-old, bookish Eastern Orthodox Serb, and his father did not approve the marriage until just before his death in 1902 [sources: Golden; Kaku; PBS].
Earlier that year, in January, the couple had a daughter named Lieserl (diminutive for Elisabeth). Marić returned to her parent's home near Novi Sad, a Serb cultural center then located in the Kingdom of Hungary but today part of Serbia's rural Vojvodina region. There she gave birth to the child, after which the couple never spoke of their daughter to others, even friends. Lieserl's fate remains a mystery to this day. The two prevalent theories hold that she died of scarlet fever or was given up for adoption [sources: Golden; Kaku; PBS].