Time Lords are indistinguishable from Humans at a glance, but there are significant internal differences. The most obvious difference is that Time Lords have two hearts, but they also have telepathic abilities and extremely long lifespans. A Time Lord can easily expect to live for centuries, and they can further extend their lives via "regeneration", a process that physically renews the Time Lord's body, giving him or her a new appearance in the process. A Time Lord can typically regenerate twelve times, giving each a true life expectancy of millenia.
Time Lords have telepathic abilities, but their extent varies among individual Time Lords, and their capabilities are difficult to determine. They seldom engage in telepathic communication, but many are adept at shielding themselves against telepathic intrusion. Time Lords can apparently speak any language like a native without effort and share this ability with their traveling companions; this ability may be linked to their telepathy, although it has also been attributed to technology in their vehicles.
At an unspecified time in the distant past, the Time Lords discovered technology to create vehicles that could travel through time and space, essentially taking passengers to any location in the universe and any date in history. Their ability to move through space and time in this manner gave them immense power. They explored space and time, eventually becoming complacent, believing that they had learned everything there was to know and retiring to live esoteric lives of contemplation on Gallifrey. Their complacency and isolationism eventually left them vulnerable to repeated invasions by less advanced civilizations.
Their final war with the Daleks brought the Time Lords to unprecedented levels of ruthlessness and brutality. They created a variety of superweapons and proxies to fight on their behalf, including "the Skaro Degradations, the Horde of Travesties, the Nightmare Child, (and) the Could-Have-Been King with his army of Meanwhiles and Never-Weres". When brought to the brink of defeat, they were prepared to use the "Ultimate Sanction", which would have destroyed space-time as we know it (along with everyone in the universe) and reduced the Time Lords to a disembodied gestalt consciousness in the aftermath.