Complex sentence: Strax is a member of the warrior Sontaran alien race forced to serve as a nurse, healing the injured as a punishment for being defeated by the Doctor during the Sontaran invasion of Earth.
Split into simpler sentences: Strax is a member of the warrior Sontaran alien race. Strax was forced to serve as a nurse, healing the injured as a punishment for being defeated by the Doctor during the Sontaran invasion of Earth.