A Time Lord on Gallifrey
The Time Lords are the Doctor's race. Two-hearted humanoids originating from the planet Gallifrey, they were the first to discover Time Travel via the Eye of Harmony, a neutralized star held at the brink of becoming a black hole. They also invented TARDISes. In the series, the Doctor often talks about his people as great inventors and a perfect example of society. However, they are often shown as corrupt politicians or mad scientists wanting power.
In the Show
The Time Lords first appeared in the War Games, where they put the Second Doctor on trial and ultimately made him regenerate. After this, they became slightly recurring characters, other than the Doctor and the Master, of course.
They had 2 hearts and a binary vascular system, allowing them to breathe in space for longer periods of time. They also had the ability to regenerate.
In the Mod
The Time Lords have appeared in the mod since November 2013, in what is called the 50th Anniversary Update. In the mod, their name is spelt 'Timelord' instead of 'Time Lord'. They are also hostile, though are planned to be changed to a neutral mob in the future. The Time Lords will also be able to regenerate in future updates.