Distance
An ultra marathon is defined as any race further than 26.2 miles (42km).
However, for the purposes of this list, since 50k is the most common "short distance" ultra marathon, only individuals who've run 50k or farther will be considered.
Verification
You must have a verified finish time from a race director to qualify for this. Self-timed races will not count.
Antarctica
There are many disputes over what counts as an ultra marathon on Antarctica. For the purposes here, ultra marathons must be completed within the Antarctic continent - outlying islands will not be considered. For more on this, see here.