The Rutan appeared in just one episode of Doctor Who back in 1977 but are surely due a return soon. The Rutan are essentially amorphous, jellyfish-like creatures that can shape shift and also have the ability to electrocute their enemies. They are also the millennia-old foes of the Sontarans and their endless war is said to have brought destruction to many parts of the galaxy. The Seventh Doctor described them as infinitely adaptable and although they are not as military driven or superior as their fierce enemies the Sontarans, they are not to be messed with. Given the popularity of anything involving Strax in the new series, and the fact that they have already re-introduced the Sontarans, a possible re-appearance from the Rutans would make perfect sense and certainly be easy to introduce. It would also give us an excuse to have a Strax-centric episode, not that we need an excuse, while it could also mean another episode based around our now favourite Victorian crime fighting trio. Also, given their love of transforming into anyone they like, wouldnt that prove a very interesting plot for the new Doctor to handle.