Who married Frederick I, Count of Berg-Altena?

Frederick I (German: Friedrich I.) (1173–1198) was a count of Berg-Altena, the later County of Mark.

Frederick was the son of Eberhard I, Count of Berg-Altena, and inherited the south-eastern territory of Altena. He married Alveradis von Krieckenbeck-Millendonk, daughter of Reiner von Krieckenbeck-Millendonk, and they had issue:

• Adolf I of Altena (c.1194–1249);
• Friedrich of Altena (fl. 1199).