Rubathon Blue was a companion of the Fifteenth Doctor in an alternate timeline.
Biography
Rubathon was a hatchling of the 57th Hemisphere Hatchlings, something which she was prideful of.
Following Ruby Sunday accidentally stepping on a butterfly in Earth's distant past, a new timeline was created in which the planet's evolutionary history was altered. Rubathon Blue took the place of Ruby Sunday in this new timeline.
The Doctor expressed alarm at this, which offended Rubathon, who threatened to kill him if he had made an "incorrect accusation" that she did something wrong. Following the Doctor's revival of the butterfly, Rubathon's timeline was negated, and Ruby Sunday was restored. Following this, the Doctor turned on the butterfly compensation switch in the TARDIS. (TV: Space Babies [+]Loading...["Space Babies (TV story)"])
Personality
Rubathon was seemingly narcissistic, believing herself to do no wrong. Upon the Doctor's exclamation of shock after the butterfly was stepped on, she sternly warned him that she would have to kill him if he were to make such an accusation.
She spoke with a posh accent, and stated her full title of "Rubathon Blue of the 57th Hemisphere Hatchlings" when scolding the Doctor. (TV: Space Babies [+]Loading...["Space Babies (TV story)"])