"Unreal is a series of first-person shooter video games developed by Epic Games. The series is also known for its exhibition of the Unreal Engine that powers the games and is available for other developers to license. As a result of Epic's focus on the engine technology, much of the creative workload such as map design has traditionally been outsourced to other studios, namely Digital Extremes. Legend Entertainment was brought in for the first game's expansion pack and its sequel, Unreal II. For the latest installment, however, Epic completed all design work in-house."
Source: Wikipedia, "Unreal_(series)", available under the CC-BY-SA License.