The Story of Vel'Koz
Vel'Koz is a Void creature, but one operating on a different principle than the others: while most Void-spawn destroy, Vel'Koz studies. His purpose, as far as can be determined, is to understand organic life in Runeterra — to learn how living things are made, how they function, what they can do, and what breaks them. He pursues this knowledge through a process of systematic dismemberment at the molecular level that his subjects experience as death but Vel'Koz regards as data collection.
His eye is a weapon and a sensor simultaneously: it fires beams of energetic force that destabilize molecular bonds, disassembling matter in ways that produce usable information about its composition. This is not cruelty in the way a human would mean cruelty. Vel'Koz has no concept of cruelty or of the experience of being disassembled. It has a concept of complete information and incomplete information, and incomplete information is a problem to be resolved.
He sends his findings back to the Void, where they serve purposes that Runeterra has not yet had to confront directly. The Void is learning. Vel'Koz is how it learns. The intelligence being accumulated about organic life in Runeterra is not for any present purpose — it is preparation for something that will be needed once the Void's primary objective is achievable. Vel'Koz doesn't speculate about that. He collects data. The application of data is someone else's problem.