Jacob Kettler (1610 - 1682)
Kettler ruled the Duchy of Courland from 1641 to 1682. Under his rule, the duchy was brought to its greatest peak in wealth... The Duke was taken prisoner by the Swedes from 1658 to 1660, during the Northern Wars. During this time, his colonies were attacked and lost and his fleet destroyed.
--From Wikipedia, which has more information and a picture:
Chart showing the number of references in each month of the diary’s entries.