From Behind The Name
Derek - Low German form of Theoderic
Theodoric - ) "ruler of the people" from Germanic şeud "people" and ric "power". Theodoric the Great was a 6th-century king of the Ostrogoths who eventually became the ruler of Italy.

From Kabalarians
The name of Derek gives you a very individual, reserved, serious nature. You stick stubbornly to your ideas or decisions, in spite of any appeals or advice; you are not willing to accept a compromise. You prefer to be alone with your own thoughts, rather than in the company of others. This name restricts spontaneity in association and the fluency of your verbal expression. When you are required to express yourself in personal matters requiring finesse and diplomacy, you feel awkward and embarrassed. Although you realize perfectly well what is expected of you, you are unable to find the right words, and hence you end up saying something inappropriate in a candid way. You can express your deeper thoughts and feelings best through writing. Your friendships and personal associations are rather restricted, being limited to those of a similar nature who can understand and accept your rather straightforward yet reserved manner. You are steadfast and loyal, and do not allow gossip or anything belittling to be said against those whom you accept in friendship. You find satisfaction in being outdoors or in getting out into nature, or in dealing with the products of the earth. There is originality and depth of thought contained in this name, particularly along practical and mathematical lines. This name can adversely affect the health of your respiratory organs, the heart and lungs. Also, you are prone to suffer from weaknesses centering in the head.

Derek's name in other languages...
Hawaiian: Keleka

Derek's name in Chinese (For a wallpaper of this image courtesy of Good Orient, click here):