A Kroot Sharper.
Kroot leaders are known as Shapers; they are generally the Kroot with the best ability for recognizing desirable traits in defeated foes and tells his Kindred (the word for a Kroot clan) what to eat to suit the task at hand. Normal Shapers guide certain adaptations in some Kroot Kindred, while other Shapers work in the Shaper Council which oversees the development and guides the Kroot Kindred's Gene Matrix.
Shapers also pay homage to the Master Shaper who is the leader of the Kroot Kindreds and holds the responsibility of allowing or rejecting certain traits into the Kindreds Gene Matrix.
For instance, a Shaper who wants his Kroot to gain muscle mass will take on campaigns against Orks to acquire the right DNA, while extensive feeding on flying predators will allow the Kroot to grow wings.