Ohm

Ohm was a (mad) Time Lord god that Savar met whilst searching for Omega within a black hole. (PDA: The Infinity Doctors)

Behind the scenes

 * OHM was also a proposed (but never used) name for Omega, as the name when rotated 180 degrees forms the word 'WHO'. Coincidentally, Ohm is a unit of measurement represented by the upper case version of the Greek letter Omega. (DW: The Three Doctors)