According to the marriage certificate issued on 14 April 972?a masterpiece of the Ottonian Renaissance?Theophanu is identified as the neptis (niece or granddaughter) of Emperor John I Tzimiskes (925?976) who was of Armenian descent. She was nevertheless of distinguished noble heritage: recent research speculates that she was the daughter of Tzimiskes' brother-in-law (from his first marriage) Constantine Skleros (c. 920?989), and of Sophia Phokaina, Tzimiskes' cousin as the daughter of Kouropalat?s Leo Phokas, brother of Emperor Nikephoros II (c. 912?969).
Holy Roman Emperor Otto the Great had requested a Byzantine princess for his son, Otto II, to seal a treaty between the Holy Roman Empire and the Eastern Roman Empire. A reference by the Pope to Emperor Nikephoros II as "Emperor of the Greeks" in a letter while Otto's ambassador, Bishop Liutprand of Cremona, was at the Byzantine court, had destroyed the first round of negotiations. With the ascension of John I Tzimiskes, who had not been personally referred to other than as Roman Emperor, the treaty negotiations were able to resume. However, not until a third delegation led by Archbishop Gero of Cologne arrived in Constantinople, were they successfully completed.
According to the Saxon chronicler Bishop Thietmar of Merseburg, Theophanu was not the virgo desiderata, the anticipated imperial princess, as the Ottonian dynasty had marked out Anna Porphyrogenita, a daughter of late Emperor Romanos II. Nevertheless, when Archbishop Gero conducted her to Rome, Emperor Otto knew that he could not refuse the offer. The young princess duly arrived in grand style in 972, with a magnificent escort including Byzantine artists, architects and artisans, and bearing great treasure (wikipedia)