BEFORE WE ACTUALLY SEE THEM ON THE SHOW...
In a distant galaxy, a species of war-like beings developed on the planet Sontar. Since their earliest days, these creatures were in love with conquest. Before they discovered interstellar travel, they were content to attempt to dominate each other. Wars were constantly erupting within their society.
Like Earth, the varied climate of Sontar created different races. Sontarans that inhabited the colder regions of the planet had one type of appearance. Whereas the denizens of warmer climes looked another way. These minor variations, of course, provided enough reason for these races to hate each other and battle endlessly.
As they warred against each other, the Sontarans were still able develop technology among all this bloodshed. They eventually managed to begin travelling in space. As they did, their society re-shaped itself. They discovered other life forms and immediately decreed them inferior. They would need to be conquered and enslaved. This was a task that required the entire planet to unify itself. Racial differences were cast aside and the Sontarans went out into the universe to plunder it.
For quite some time, this went well for them. But, eventually, they encountered an equally-xenophobic race that were making their way through the galaxy on an invasion campaign of their own. The Rutans provided a challenge that was almost too great for the mighty Sontarans. The two warrior races began to clash.
THE SONTARANS WE SEE TODAY
Much to the shock of the Sontarans, the Rutans were actually able to push them back in their advance upon the Universe. This Host of amorphous jelly-fish like creatures proved not only difficult to kill, but also quite lethal in the way they attacked. The Sontarans were forced to retreat against their might.
And so, genetics became the great obsession for the Sontaran military scientists. The species re-designed itself. Taking after their enemy, they became creatures that fed off pure energy to survive rather than consumption of food. They did this by developing a probic vent in the back of the neck to use as a feedline for the energy. This also became known as a Sontaran's only weakness. Their genetically-modified bodies and space armour was so resilient, that they were impervious to most forms of attack.
But these genetic improvements were not enough. Sheer weight of numbers was the only way to crush the Rutan Host. In combat, it would take dozens of Sontarans just to down one Rutan. Having made the perfect warrior's body, Sontaran scientists then went on to master the cloning process. Millions of Sontarans could be hatched on a regular basis and programmed from an early age to become ruthless warriors dedicated to the destruction of the enemy. We see slight variations to those clones (ie: Sontarans in Two Doctors seem considerably taller), of course, because there were different races on Sontar. Each race got their own clone batch.
At last, the Sontarans were able to pose a legitimate threat to their foes. Their campaigns began to advance again.The war between the Sontarans and the Rutans could begin in deadly earnest.
THE CONUNDRUM OF INVASION OF TIME
Up until Series 4 of the New Series, placing The Invasion of Time in this timeline was pretty simple. It seemed to me that this would be the final story in their chronology. Which made sense. The Sontarans would have to be at their greatest, most advanced stage to penetrate that Transduction Shield and conquer the Panopticon. It helped that this is one of the few Sontaran stories that doesn't mention the Rutans. In my imagination, it signified that they had finally beaten their greatest enemy and could move on to bigger and better things like the conquest of Gallifrey. Again, this made me believe that this must have taken place at the end of all the other Sontaran stories we've seen.
But then we get The Sontaran Stratagem - which takes place sometime around 2008. General Staal laments toward the end of the episode of how the Sontarans were not allowed to participate in the Time Wars. Up until that moment, I liked to believe that the Time Wars took place in the far-flung future so that Invasion of Time could still fit my version of Sontaran history. Sometime after the events of Sontaran Experiment the Sontarans lead an aggravated assault on Gallifrey. But Staal's complaint indicates that the Time Wars probably happened in the 2000s. I suppose we could set up all kinds of timey whimey arguments that would still support my initial view. These are time-travelling Sontarans that have come back to the past. Or the Time Wars are in their own special time zone. Or Invasion of Time actually took place in an alternative reality where the Time Wars never happened. There's lots of directions we can take this in. But I prefer to just say that Invasion of Time takes place in a different point of Sontaran history than I had previously envisioned.
So now, I put Invasion of Time at the beginning of the timeline. At some point during their war against the Rutans, the Sontarans are winning and can start concentrating on side-campaigns. Seeing the tactical advantage that time travel could afford them, they begin experiments in the Fourth Dimension. This leads them to discovering the existence of the Time Lords. Sontaran mentality being what it is, the decision is made to devise a way to invade Gallifrey. A false alliance with the Vardans is forged and their plans are set in motion. The Invasion of Time takes place.
FIRST CONTACT WITH EARTH
A specific date for Invasion of Time is difficult to determine - but we're assuming it takes place, at least, a short while before the next story in their timeline: The Time Warrior.
Linx is in possession of an osmic projector - a sort of primitive time scoop with limited range. Perhaps the Sontarans managed to steal some of the secrets of the Time Lords during their short-lived occupation. Or, perhaps, Sontaran scientists made these discoveries on their own. Either way, Sontarans are now capable of short jumps through time.
There is no indication that it's time travel that brought Linx to Irongron's castle sometime during the 1200s so we have to assume that this is the proper era in which this tale takes place. Linx does talk to the Doctor about the little knowledge he has about Time Lord society. He doesn't have much good to say about them. According to the data he's been given, they are not even worth being conquered. We can safely assume this was propaganda created to cover up a defeat. It also gets Invasion to fit a bit more nicely at the beginning of this timescale.
Fortunately for Earth, the Sontarans see no real use for this world. Linx's crashlanding was a fluke. The strange little blue/green planet is too far out of the way of the main war. Of course, seven-or-so centuries later, a Rutan scout would be sent to investigate this part of the galaxy and have its efforts thwarted by the Doctor, too.
THE WEAKENING OF THE SONTARAN STRAIN
Sometime between The Time Warrior and Horror of Fang Rock, the Rutans make their own technological strides to combat the advantages that their enemies were holding over them. They don't seem to discover time travel but they become masters at shapeshifting. This ability to perfectly duplicate other life forms changes the tides of battle. The Sontarans are losing again. They need to take drastic steps to increase their numbers even more. Those super-resilient bodies are intentionally weakened so that larger batches of warriors can be hatched. They are not told, of course, that they are genetically inferior but we see evidence of greater vulnerability during the next few stories.
Deciding the osmic projector is not enough, the Sontarans decide they need to enhance their time travel abilities. They strike an uneasy alliance with Dastari and Chessene from Space Station Chimera to steal the Kartz/Reimer time travel module. They also abduct a Time Lord (who turns out to be the Doctor) to discover where his Rassilon Imprimature lies in his genetic code. Their operations lead them to Earth in 1984. The events of The Two Doctors take place. Like The Time Warrior, there is no implication of time travel so we can assume this is the proper year in which this adventure transpires. It is here where we see the first evidence of weaker Sontarans. They now seem to be vulnerable to coronic acid. Jamie's knife also seems to be capable of doing some legitimate harm to Group Marshal Stike. Information stated about Sontarans in previous stories insinuate that they are, generally, invulnerable to such attacks. That the probic vent is the only way to take them down (or a significantly large explosion). But this doesn't seem to be the case, anymore. Although, Stike does seem to recover from his knife wound fairly quickly. So this particular generation of Sontaran is still reasonably strong.
Over the next few decades, though, the gene-strain is diluted even further to swell their numbers. The Sontarans that attempt to convert Earth into a clone hatchery in 2008(ish) are now even vulnerable to a mere bullet. We have never seen such weak Sontarans as we do in The Sontaran Stratagem/Poison Sky. I like to think that there's a legitimate reason for this inconsistency. Which is why I came up with my silly weakening of the gene strain theory.
NEXT CONTACT WITH EARTH
And now we must jump forward a considerable amount of time to The Sontaran Experiment. Dating this particular story can be a bit tricky. It takes place sometime after all the solar flare trouble that Earth experiences in the 30th Century that gets discussed in stories like Ark In Space and Beast Below. But it needs to occur before we see the Earth that is, once more, thriving in the 40th Century in stories like The Dalek Masterplan.
A general impression is given that the sleepers on Nerva Beacon were meant to stay in hibernation for 5 000 years. The Doctor claims they've overslept by a few thousand years due to Wiirn sabotage. So let's say Sontaran Experiment takes place sometime in the 38th Century. That gives enough time for the planet to re-colonize and show real political strength as Mavic Chen's dastardly schemes start hatching.
While the Sontarans learnt a bit about humans way back in the late 20th/early 21st Century, that knowledge has been intentionally lost. Again, Sontaran propaganda always ascertains that defeats were forgotten. But, once more, it's become strategically-sound to investigate humanity's corner of the universe. So Field Major Styre is sent off to assess humans and uncover their weaknesses.
Why does Styre have five fingers while all other Sontarans have three? Sontaran scientists are always assigned five fingers at their hatching so they can better handle delicate scientific apparatus.
Although most of his stories take place on 18th Century Earth, Strax becomes Madame Vastra's butler through a convenient trip in time shortly after A Good Man Goes To War. Our favorite bumbling Sontaran really hails from the 41st Century. The first time we see him, Moff is nice enough to display that it is the Year 4037. We must assume that, even without Styre's report, the war with Earth and its associated colonies eventually proceeds. Strax's penance at the Battle of Zaruthrstra seems to be a definite conflict between Sontarans and humans. Interestingly enough, Sontaran nurses appear to be completely neutral on the field of battle. Willing to help either side with their medical needs.
After being transported to Demon's Run, Strax is killed and then resurrected. We're still not entirely sure how. Perhaps some kind of cloning trick that actually seems to downgrade him, slightly. Like taking a photocopy of a photocopy. But all his adventures in Victorian London that we see in The Snowmen, The Crimson Horror, The Name of the Doctor and Deep Breath are the result of a trip through time. Strax really comes from one of the latest points in the Sontaran timeline.
It may be entirely possible that the Sontaran gene-pool has, once again, been compromised. Strax is seen to be rendered unconscious in a bar brawl during Name of the Doctor by a blow to the front of his face by a shovel rather than to the probic vent (it's difficult to ascertain - given the fact that the attack is filmed as a pov shot). This weakness, however, might also be due to whatever was done to him at his resurrection. We can't be sure...
NEW SERIES CAMEOS
We see the Sontarans making a few brief cameos in the New Series along with a Rogue's Gallery of other recurring villains. Since the Daleks were there too, I've mapped out the timeline of those appearances during my post on their history. Putting the Sontarans into that timeline won't be difficult.
While there's no real indication of an exact date, I estimate that the Alliance to seal the Doctor in the Box of Pandorica must have happened sometime after the 40th Century. As I explained in my summary of Dalek History, the various aliens are from the future but they travel back in time to Stonehenge in 102 AD. More than likely, the Daleks set up some huge time corridor to get them all there. The Sontarans, with their own knowledge of time travel, may have assisted. Or, proud warriors that they are, they may have gotten there on their own.
Finally, there's the blockade around Trenzalore in Time of the Doctor. Again, no real date can be given but I estimate that it takes place sometime after the events of Pandorica Opens/Big Bang. I could go into detail about about how it all lines up in Dalek History but it's not particularly efficient to re-state it all here when there's another post that has it all, already. I'll post a link at the bottom if you want to look it over.
All righty, then. Sontaran History charted. We'll deal with other recurring baddies in future posts. There's still quite a few of them to sort out. Oh yeah, here's that link to Dalek History that explains that last section a bit better: