The Daleks were created by writer Terry Nation, the brain behind much classic British science fiction. The story goes that Nation was working for comedy genius Tony Hancock when the BBC asked him to write for Doctor Who. Not wanting to be involved with a kids show Nation turned them down. Shortly afterwards Hancock and Nation had a "disagreement" and parted company. Finding himself without work Nation reluctantly took the job with the BBC - and gave us the greatest SF creation of all time.
Today the original Kaled race has mutated and devolved to something akin to a lump of green slime inside the Dalek exoskeleton. In the words of the Doctor they are: "little green blobs in bonded polycarbide armour". This armour has taken various colours over the years but for many fans the outfits that looks best on a Dalek remains simple silver and basic black.
The Daleks exist solely to conquer and subjugate "lesser" creatures. Any who refuse to obey are ruthlessly exterminated. Unlike the Cybermen the Daleks lack any sublety and rely on simple brute force.
(Having said that, they did seem to have a less aggressive approach to Jo Grant / Katy Manning, at least so it seems from one famous photo!)
In the new Doctor Who series the Daleks were initially believed to have been wiped out in the great Time War but - like the proverbial bad penny - returned to once more threaten the Doctor.
The relationship between Davros and the Daleks is long and complex. At times they have recognised him as their creator and hence their leader, at others they have schemed against him. Some Dalek factions follow not Davros but the Emperor Dalek - others refer to Davros as Emperor. There is a history of fighting amongst the different factions with various generations of Dalek considering themselves the true master race and the others inferior mutants. As companion Ace said: "They hate each others' chromosomes. War to the death."
At the time of writing Davros has not yet appeared in the new Doctor Who series.