They absorbed energy via the probic vent on the back of their necks. This vent was also their crucial weakness, as any sudden blow to the vent would stun them. The penetration of a sharp object into the vent would kill them. (TV: The Time Warrior, The Invasion of Time, et. al.) Tampering with the energy source could also lead to a reversal effect that could destroy a Sontaran from the inside out. (TV: The Sontaran Experiment)
Sontarans could live into their eighties, but their culture meant that they were unlikely to do so. (AUDIO: Old Soldiers)
The highest honour for a Sontaran was to serve in the Imperial Sontaran Fleet and to be disallowed soldiering was the most dishonourable fate for a Sontaran. (COMIC: The Betrothal of Sontar) Taking care of the sick and wounded was a humiliating concept. (TV: A Good Man Goes to War) Fighting for other species was an equally dishonourable fate. (TV: Enemy of the Bane) Sontarans did not fear death and they would rather be court-martialled than show pain. They considered it honourable to face battle "open skinned", without a helmet on. (TV: The Sontaran Stratagem/The Poison Sky)
Despite being a clone race, the Sontarans still retained the concept of betrothal, which was roughly analogous to ending hostilities by killing your enemy. (COMIC: The Betrothal of Sontar) Within their society, there was a rigid clan structure, with clans having different genetic markers. (PROSE: Lords of the Storm) The clans vied for power. Some had great influence, such as the Gunnar Clan. (PROSE: Shakedown) Sontarans were known for Quicksand Wrestling. (TV: Enemy of the Bane)
Some Sontarans bore eponyms, relating to past victories and events that had occurred in their lives. Sontarans would often introduce themselves by their full name and rank and/or title. The Tenth Doctor pointed out that a title such as Staal's ("General Staal the Undefeated") would no longer be accurate if he did get defeated, joking that that would make him "General Staal the Not-Quite-So-Undefeated-But-Never-Mind." (TV: The Sontaran Stratagem/The Poison Sky, The Last Sontaran)
If a Sontaran opposed the decision of their commanding officer, they could duel to the death to decide which would be the leader. (PROSE: The Taking of Chelsea 426)
Sontarans considered informing a person that they looked forward to someday killing them on the battlefield a compliment. (TV: A Good Man Goes to War)
Due to their dedication to warfare and short lifespan, Strax considered a twelve year life to be a long one amongst his species. (TV: A Good Man Goes to War)
Note that the ranks are listed in presumed order of seniority in relation to Earth armed forces. The precise order is pure speculation.
The Sontarans were reasonably advanced, though all their technology was designed for use in the war with the Rutan Host. They often used spherical spaceships and could make advanced robots for various purposes.
When on a planet, the Sontarans would travel by the means of aircraft. These aircraft looked like the bottom half of a Sontaran ship, with seats and controls on the top half. (COMIC: The Betrothal of Sontar)
Sontarans wore distinctive battle armour, which resembled a thick and bulky grey space suit. Their helmets were dome-shaped and almost featureless except for two eye holes and a small, flat crest running from the forehead to the back of the neck. They generally carried around their rod-like weapon and a translating device. (TV: The Time Warrior)
The Sontarans were capable of creating around a million clones every four minutes, which allowed them to sustain massive casualties. (TV: The Time Warrior) These clones were fed using the probic vent, which was the Sontaran's only weak spot. These clones were grown in vats and were nourished by sezerfine gas. (TV: The Poison Sky)
The Kaveetch were the original natives of Sontar, and also considered themselves "Sontarans" (just like Humans could be called "Earthlings"). They appeared more like humans. (AUDIO: The First Sontarans)
After a war with the Rutan Host had reached a stalemate, Meredith Roath proposed the creation of a clone army, namely the Sontaran clones. Within weeks, the clones were not only fighting on the front lines but had turned the tide of the war firmly in the Kaveetch's favour. (AUDIO: The First Sontarans)
Even the existence of the Kaveetch was eventually erased from the Sontarans' official history (AUDIO: The First Sontarans). According to the Sontarans themselves, before enountering the Rutans, they were split into clans, which would fight amongst themselves. The survivors of these civil wars joined forces and set their aggression on aliens instead. (PROSE: Shakedown)
Later, in the year 1522 AD, a Sontaran scoutship crash landed on Earth in China. As a result of the incident, their hyperspace transmitter was damaged and they required a replacement crystal in order to summon reinforcements as well as to take over the planet. There, they formed a partnership with the Abbot Hsiang and Yueh who knew them as the "bronze men" where they used their hypnotic technology to test enhance his fighting abilities.
The Emperor of China learnt of the enhanced fighting skills of the monks and came for a demonstration. This was all part of a plan by the Sontarans to kill the Chinese Emperor as he possessed a quartz crystal sufficient to power the hyperspace transmitter and thus placed a hypnotic suggestion designed to turn the monks against the Emperor in order to kill him.
However, the Fourth Doctor intervened and had K9 recorded the trigger words and broke the spell but not before Chang went into a berserker attack that killed the Sontarans as a result of him hearing the command phrase once. (COMIC: Dragon's Claw)
In 1605, a group of Sontarans came searching for a crashed Rutan ship buried under the Houses of Parliament that contained two doomsday weapons capable of wiping out an entire species. Both the Sontarans and the Rutans raced to retrieve them but the Eleventh Doctor reached them first, modified them and gave one to each party and told them they could use it on the other but faced a risk of killing their own species instead. (GAME: The Gunpowder Plot)
Sontaran soldier Brak visited Earth in 1916 and witnessed the Battle of the Somme. He was captured by British soldiers and imprisoned for eighty years, during which he created powerful weapons for humanity in the hope that they would tear each other apart. (AUDIO: Old Soldiers)
In the 1980s, the Sontaran Warburg investigated the possibility of using time ships in order to win the war. At the same point in time they were involved in a battle with the Rutans in the Madillon Cluster. Neither attempt was successful. (TV: The Two Doctors)
The Sontarans used a form of hypnosis on the workers of the ATMOS factory, forcing them to start shipping out devices that contained gases poisonous to humans, contained inside plates attached to the Sat-navs they sold. When the Tenth Doctor attempted to meddle, the Sontarans activated all the devices already deployed in cars, releasing the poison gas and choking people nearby. (TV: The Sontaran Stratagem)
The gas was burnt away by the Doctor's use of an atmospheric converter and Rattigan, having been betrayed, sacrificed his life by using the converter to destroy the fleet. (TV: The Poison Sky)
Following this failure, Kaagh became a mercenary for the Bane. He met Mrs Wormwood while looking for the remains of Horath and they agreed to work together. After finding the mind of Horath, he followed Wormwood to Earth, where they took the Tunguska Scroll from Sarah Jane and kidnapped Luke Smith. The alliance started to break down when Mrs Wormwood sided with Luke over Kaagh, ending when she betrayed and disabled him. Seeing that he had lost, he dragged Wormwood into the wormhole containing Horath. (TV: Enemy of the Bane)
At some point during the 26th century, the Sontarans sent in Commander Steg to conquer Jekkar in order to create a buffer around Sontar. Though he had no difficulty with the humans, the Jekkari, led by the Seventh Doctor, were able to fight back effectively. The surviving Sontarans destroyed their bases and abandoned the planet. (PROSE: Shakedown)
Some time later, an expedition was made to go to Sentarion and take advantage of the wormhole connecting it and Ruta III to kill the Rutan Queen. Though the Sontarans tried to keep this information classified, a Rutan spy known as Karne was able to learn that the information had leaked out and tried to return to the Rutans.
Commander Steg was sent in to redeem himself and kill Karne. He was able to track it to the space yachtTiger Moth, where it had hidden in the ship. During the course of his investigations, his soldiers were whittled down by Karne and the human crew. Eventually, Karne was killed and all the Sontarans were believed to be killed. In reality, Karne was able to clone himself before his death and Steg was able to pull through. (HOMEVID: Shakedown: Return of the Sontarans, PROSE: Shakedown)
The second Karne was to able escape to Sentarion, followed by the Seventh Doctor, his companions and the survivors from the Tiger Moth. Commander Steg was able to follow them with a War-Wheel and forced the Doctor to open to wormhole to Ruta III. The War-Wheel was sent through, but the Doctor was able to reverse the polarity of the wormhole, meaning the War-Wheel would never get to Ruta III. When Steg tried to kill the Doctor in revenge, a fight began, leading to the death of Karne and the Sontaran forces. (PROSE: Shakedown)
Also at some point during the 26th century, the Sontarans and Rutans took their war to the colony Chelsea 426. The Fourth Sontaran Intelligence Division, led by General Kade, were given the mission of hunting down Rutans that were at the time taking over human bodies. The Tenth Doctor was present during the event and while he did not side with either waring party, he did stop the Rutans, after which the Sontarans left. However, there was evidence that the Sontaran Division's trouble with the Rutans was not fully over after their ship left the colony. (PROSE: The Taking of Chelsea 426)
During either the 25th or 26th century, the Rutans destroyed the Sontaran homeworld, Sontar, with photonic bombs, though some escaped with the Sontaran racepool. At the same time, the Sontarans encountered the Pureblood Sontarans. Due to the intervention of the Seventh Doctor, the cloned and pureblood Sontarans decided to pool their resources and Marshal Stave promised to remove the Sontarans' memory of humans from the racepool. (COMIC: Pureblood)
Many thousands of years after the 20th century, at a time when the Earth had been abandoned for 10,000 years, the Sontarans were separated from the many human worlds like GalSec throughout Mutter's Spiral by a buffer zone. The Grand Strategic Council planned to invade the galaxy, but they had to abandon that plan when a scout, Field Major Styre, was killed while trying to assess the strengths and weaknesses of the humans. After this, the Fourth Doctor bluffed, telling the Sontarans that their battle plans had been captured, so they would have to call off their invasion. (TV: The Sontaran Experiment)
The Sontaran mining ship Betrothal of Sontar was sent to Serac as a form of demotion. Colonel Snathe, a pureblood Sontaran, believed that the Thanatos was located on Serac, but his attempts to find it were unsuccessful and crew became restless and insubordinate. When the Tenth Doctor arrived, Snathe forced him to find the Thanatos - but when Snathe tried to control it, the Thanatos decided that the Sontarans were stagnant and Sontar needed to be destroyed. Though Lerox showed that there was still hope for the Sontarans, Snathe was killed when the Inuk shoved him outside during a Silverfire. (COMIC: The Betrothal of Sontar)
The Carpalian Witch's favourite hunt was when she hunted a Sontaran. Since her pheromonal lure was ineffective, she waited in his ship for 6 weeks until she stabbed him in the probic vent when he was about recharge. (PROSE: The Doctor Trap)
An unnamed planet (defined as a "worthless rock" by the Sontarans) was an outpost of the Sontaran-Rutan war. The Fifth Doctor tried to advise the local commander Strock a strategy to avoid useless loss of soldiers. (COMIC: Prisoners of Time)
The Sontarans were among the many species drawn to Trenzalore by the asking of the First Question but locked out of the planet by the force field put up by the Papal Mainframe. Two Sontarans attempted to bypass the force field during the Siege of Trenzalore by putting on an invisibility cloak, but the Doctor used his sonic screwdriver to make them visible to the Papal Mainframe, which they were then destroyed by. Conforming to protocol, the Mainframe apologised for their deaths and selected an appropriate afterlife. Later, the Daleks attacked the Mainframe and broke through the force field. The Sontarans followed them to the surface and either died in the fighting or possibly retreated. (TV: The Time of the Doctor)
When these encounters with the Time Lords occurred is unknown, due to the difficulty in dating the Time Lord stories.