text: This ruler's brother Thankmar revolted against him before being defeated in Eresburg.
full_question: This ruler's brother Thankmar revolted against him before being defeated in Eresburg. This man had his son and successor married to Theophano to conclude peace talks with Byzantium. He had several successful campaigns against the Slavs with the help of Gero the Great. This husband of Adelaide survived a battle that led to the deaths of Conrad the Red as well as Bulcsu and the chieftains Lel and Sur, who were executed at Regensburg. Seven years after he defeated the Magyars at Lechfeld, this man was crowned in 962 by Pope John XII. For 10 points name this Duke of Saxony who became the first German Holy Roman Emperor.
first_sentence: This ruler's brother Thankmar revolted against him before being defeated in Eresburg.
raw_answer: Otto I [or Otto the Great; prompt on "Otto"]