Diederik of Hamaland (970-Upladen, April 7, 1017/18), also called Diederik I van Kleef, was Count of Hamaland of -1014, from the genus of Immedingen. His father, Immed IV of Hamaland, also known as Immed van Kleef, was the first husband of Adela van Hamaland, daughter of Count Wichman IV. Diederik was their oldest son.
At the death of his father Immed in 983, Diederik was still very young to actually take over the county. The second spouse of his mother, Balderik van Duffelgouw, tried to continue as ruler. Diederik was killed in 1017 at Upladen, the castle of his stepfather Balderik. Balderik now also called Count of Hamaland, although it is not clear to what extent he really was recognized as a grave.
Diederik also acquired the county of Teisterbant, possibly by a marriage with a daughter of Count Unruoch of Teisterbant.
Diederik left several daughters. The oldest, Addila, married Godfried, Duke of Lower Lorraine (1012-1023). This eventually followed him as a tomb of Hamaland.
A younger daughter married about 1025 near Antoing at Tournai with Gerard II Flamens († for 1052). This could also be attributed to parts of Hamaland. When the genus of Verdun fell in disgrace and "Godfried with the Beard" was defeated by Emperor Hendrik III in 1046, his son, Gerard III († before 1058), could ultimately benefit from this.
The first Count of Kleef, Rutger I, was the brother of Gerard van Antoing. Diederik and his father are often referred to as "van Kleef" in modern genealogies, but although they had possessions in that region, they were not yet digged by Kleef.
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