The Time Lords intercepted the transmat beam taking the Fourth Doctor, Sarah Jane Smith, and Harry Sullivan back to Nerva and deposit them instead on the planet Skaro at an early point in its history. There a Time Lord gives the Doctor both a mission to prevent or alter the Daleks' development so that they become less of a threat to the universe and a time ring that will enable him and his companions to return to the TARDIS once this is done.

Skaro is currently in the grip of a long war of attrition between its two humanoid powers, the Kaleds and the Thals. The Kaleds' chief scientist,

 Davros, had been experimenting to discover the final form into which his race will mutate, as contamination from the nuclear and biological weapons used in the war has already begun to accelerate the process. This final form is weak and crippled: no more than brains with tentacal-like appendages and with no hope of survival on their own. His solution is to remove all emotions pertaining to weakness, a category in which he groups such emotions as compassion, mercy and kindness.  Davros devises a protective casing in which they can continue to survive. This so called "Mark III travel machines" is instantly recognised by the Fourth Doctor and Sarah as a Dalek, an anagram of Kaled.

Escaping from the bunker where Davros and his Scientific Elite are based, the Fourth Doctor and Harry persuade the Kaled leaders to put the Dalek experiments on hold. Davros retaliates by conspiring with the Thals to destroy the Kaled city with a rocket. He then activates the Daleks and orders them to wipe out the Thals.

Some members of the Elite revolt, protesting at the genetic alterations that Davros has made to the Daleks, and they too are exterminated. The Daleks then seize control, killing the remainder of the Elite and ultimately Davros himself. Thal survivors detonate explosives at the entrance to the bunker, sealing the Daleks inside. After this, The Fourth Doctor, Sarah, and Harry depart Skaro believing they have set the Daleks progress back about a thousand years. 

War with the Movellans:

A stalemate arose in an interplanetary war that the Daleks were waging against the robotic Movellans. In an attempt to break this impasse, the Daleks returned to Skaro to look for their creator, Davros. The Fourth Doctor and a newly-regenerated Romana arrive on Skaro and discover that the Daleks are using explosive charges and a group of humanoid slave workers to mine the planet in their search. A force of Movellans has also arrived on Skaro, determined to thwart the Daleks' plan.  

Davros is found in the ruins of the old Kaled city and immediately revives, his life support systems having held him in suspended animation ever since his apparent death. He quickly deduces that the battle computers of the two warring races are locked in a logical stalemate and that he can break this by introducing an element of intuition. The Movellans, having reached the same conclusion, want the Fourth Doctor to do likewise for them.

Davros attempts to destroy the Movellan ship using a suicide squad of Daleks loaded with bombs, but the Fourth Doctor returns to the Kaled city and tricks him into inadvertently detonating them before they reach their target. The Movellans are deactivated and Davros is cryogenically frozen on board their ship until the freed slave workers can take him to Earth and ensure that he is put on trial for his crimes.

Release:

The TARDIS becomes caught in a time corridor but the Fifth Doctor manages to free it and it then materialises in present day London within sight of Tower Bridge. Investigating some nearby warehouses, the travellers stumble into a trap that the Daleks have set for them.

A small Dalek force aided by human mercenaries also attack a space station orbiting Earth in the future. Their aim is to rescue their creator, Davros, who has been held there in suspended animation since his capture by humanity. They want him to help them find an antidote to an anti-Dalek virus created by the Movellans. The creation of this viral weapon had been the mentioned during Davros' interrogation of the Fourth Doctor when they were on Skaro. In addition, the Daleks have constructed android duplicates and installed some of them in key positions of authority on Earth. They now intend to send duplicates of the Fifth Doctor and his companions to Gallifrey in order to assassinate the High Council of the Time Lords.

Believing his creations to be treacherous, Davros begins using mind control on Daleks and humans.  Davros is unable to find a cure for the virus but has an escape pod ready in case of problems. Ultimately, he releases the virus to kill off the Daleks before they can exterminate him. However, Davros apparently succumbs to the virus himself before he can escape, his physiology being close enough to that of the Daleks for the virus to affect him.

All the Daleks' plans ultimately fail, however, as one of their duplicate humans, Stien, rebels and destroys the space station and Commander Lytton, an alien mercenary working for the Daleks, escapes to present day Earth.  

The Great Healer:

 The Sixth Doctor and Peri arrive on the planet Necros where, in a funeral and cryogenic preservation facility called Tranquil Repose, the wealthy can have their newly-deceased bodies cryogenically frozen until such time as medical science can cure whatever killed them.

 The Sixth Doctor wishes to pay his last respects to his friend Professor Arthur Stengos, and also to assuage some nagging suspicions about the man's death. His suspicions prove justified, as it turns out that this is just a ruse to lure him into a trap.

"The Great Healer", the mastermind of  Tranquil Repose is revealed to be Davros. He is using the organic material in the cryogenic storage units both as the raw material for the synthetic food that is Necros's biggest export and also to create a whole new army of Daleks loyal to him with which to take control of the universe. These new Daleks are distinguished from the original Daleks by their white and gold livery and slightly changed design.

At first Davroses appears to be only a head in a tank. The real Davros, however, emerges from hiding, in his usual chair, when the decoy is assassinated. His chair can now hover, he can move his neck, and he can fire electric bolts from his hand. The hand is later shot off in a fight and Davros flees.

Another party of Daleks arrive, those loyal to the Dalek Supreme. These original Daleks have arrived to defeat the new Daleks and transport Davros to face trial on Skaro. A battle between Dalek forces soon begins, while the inhabitants of the mortuary attempt to flee. The lower levels of Tranquil Repose are destroyed in an huge explosion, as well as all of Davros' new Daleks. 

The Dalek Civil War:

The TARDIS arrives in London in November 1963, where the Seventh Doctor and Ace discover that two rival factions of Daleks - one loyal to the Dalek Emperor, the white and gold Daleks now based on Skaro and termed "Imperial Daleks"; one loyal to the Dalek Supreme, the original grey Daleks now termed "Renegade Daleks"- are seeking the Hand of Omega, a powerful Time Lord device that the First Doctor hid there during an earlier sojourn on Earth.

The Daleks are focusing their search around Coal Hill School - the school that the Doctor's grand-daughter Susan attended - while a military unit led by Group Captain Gilmore is attempting to resist their incursions. The Seventh Doctor tries to keep Gilmore and his team out of harm's way while the two Dalek factions battle each other for control of the Hand.

 The Imperial Daleks eventually overpower those led by the Dalek Supreme and capture the device. The Dalek Emperor is revealed to be Davros, having been physically transplanted into a customised Dalek casing. Davros had hoped to use the Hand to transform the sun of the Dalek homeworld Skaro into a power source for time travel. The Seventh Doctor begs him not to use the Hand against the Earth, but is ignored. However, this is just the final ruse in a complex trap laid by the Time Lord to defeat his old adversaries. He had altered the Hand's programming so that instead of enhancing Skaro's sun, the Hand turned it supernova, obliterating Skaro and, presumably, the Daleks themselves. Just before the ships are destroyed, however, Davros takes an escape pod and flees. The Seventh Doctor then confronts the Dalek Supreme and causes it to self-destruct by convincing it that it is the sole surviving member of its race.

Time War and Beyond:

Davros was believed to have been killed during the first year of the Time War. Dalek Caan was able, however,  to use an emergency temporal shift to go to the events of the Time War, a feat thought impossible due to the events having been 'time-locked'. Caan was able to save Davros, but consequently, the Time Vortex was forced through his mind. This both drove him insane and endowed him with precognitive abilities.

Davros has a cybernetic hand, replacing the one that was destroyed. He can still fire energy bolts through it. Davros uses cells from his own body to breed a new Dalek race. He uses so much of himself that he has little skin and flesh left on his chest and his ribcage and internal organs are visible. Under his guidance, the Daleks 'steal' 27 planets, including Earth, and hide them in the Medusa Cascade, one second out of sync with the rest of the universe.

It is implied by the Tenth Doctor, however,  that Davros is not in control of the Daleks and is instead being kept prisoner in the Vault, having been overthrown, again, and kept around to give his scientific knowledge. The Tenth Doctor taunts him as being their "pet". With Davros' knowledge, the Daleks have created a "reality bomb" that would use the stolen planets as a beacon to cause all matter to dissolve into its atoms, wiping out all of existence except for the Daleks and the Crucible: he declares this to be his "ultimate victory". It turns out, however, that he and the Daleks are being misled and betrayed by Dalek Caan who is using his prophecies and influence to bring the Doctor and Donna together, causing the Daleks' destruction.

Davros is seemingly killed when the Crucible is destroyed. Just before his "death", the Tenth Doctor offers to take Davros to safety, but Davros, screaming in fury, refuses, and names the Doctor as being responsible for the destruction, calling him the "destroyer of worlds"; he previously had taunted and demoralised the Tenth Doctor as being responsible for turning his companions into killers and having caused the deaths of countless people, comparing the Tenth Doctor to himself.