Hatto soon became known to the
German king, Arnulf, who appointed him archbishop of
Mainz in 891, and he became such a trustworthy and loyal counsellor that he was popularly called the heart of the king. He presided over the important
synod at
Tribur in 895 and accompanied the king to
Italy in 894 and 895, where he was received with great favor by Pope Formosus. In 899, when Arnulf died, Hatto became regent of the Empire and guardian of the young king,
Louis the Child, whose authority he compelled
Zwentibold, duke of
Lorraine, an illegitimate son of Arnulf, to recognize. ==Execution of Adalbert of Babenberg==