Silurians

The Silurians or Eocenes are homoreptillian creatures. They were the Earth's previous rulers and became very technologically advanced ages before the dawn of humanity. However, in one point in time their astrologists noticed a planet sized crater coming onto a collision coarse with Earth. Fearing the survival of their species, they fled under the Earth and went into a state of suspended animation until the aftermath of the oncoming apocalypse was over with.

However, it turned out it was in face the moon coming into alignment with the Earth they were seeing... The disaster never came, and they were never given a chance to reclaim the Earth until it was already occupied again.

Human activities have sometimes awakened dormant Silurian hibernation chambers, such as submarine warfare that stirred the awakening of a homoreptilian counterpart of the Silurian called "The Sea Devils". The Silurians do not often take kindly to the homo sapiens that have stolen their world from them, and many times in the past isolated groups of them awakened from their hibernation attempt to destroy the Earth through various methods like forcing humans to go to nuclear war with each other...

Luckily, they have failed all of their past attempts to destroy humanity. And during their most recent activity where an entire Silurian city was revived by the disturbance from a drilling company, the 11th regeneration of the Doctor was able to derail a war between the humans and Silurians, and was nearly able to work out a peace treaty with the Silurian Emperor until the news that his daughter was killed by a mother human, who in her own defense only wanted to protect her son.

Both humankind and Silurians first viewed each other as inferior animals with no right over occupation of the planet, however the Doctor was able to convince both of their respected ambassadors into reasoning with one another. And in the end the Silurian race has went into hibernation one more time for one thousand years, and humanity was required to ready themselves for when the time comes for their reawakening... They felt if properly prepared for the occasion, that humankind and the homoreptilians might be able to coexist in the future... However some had their doubts at that, since humankind can hardly coexist with itself.