Where did this guy come from? Why does he look like that? These questions have not been directly addressed much in his six appearances throughout Televised Doctor Who, but rather through other spin-off media such as novels, comics, and audio dramas. He is a Kaled, a scientist from the planet Skaro--who once looked rather human. His appearance was a result of a bombardment from the Kaled's enemies, the Thals, which left him scarred and crippled. He is completely convinced that his creations are the pinnacle of superiority.
The 1975 serial Genesis of the Daleks is recommended watching for any Doctor Who fan who is curious about the origin of the Daleks. The Time Lords enlist the Fourth Doctor on a mission to Skaro's distant past to stop the creation of the Daleks. Clearly he did not succeed, but this story features the first appearance of Davros and explains the situation on the planet at the time and why the Daleks were created.
Davros returns in several other serials, however there aren't many earthshaking revelations about him or the Daleks. It seems the same thing happens over and over: The Daleks bring him back because they need him for some reason, Davros tries to regain control of them, the Daleks pretend to agree to his terms, than betray him again, The Doctor stops Davros and the Daleks and whatever they were up to, but he escapes, again....something like that.
Here are all of Davros's Television appearances.
- Season 12, 1975, Fourth Doctor Genesis of the Daleks
- Season 17, 1979, Fourth Doctor Destiny of the Daleks
- Season 21, 1984, Fifth Doctor Resurrection of the Daleks
- Season 22, 1985, Sixth Doctor Revelation of the Daleks
- Season 25, 1988, Seventh Doctor Remembrance of the Daleks
- Series 4, 2008, Tenth Doctor The Stolen Earth/Journey's End
Here is the TARDIS Data Core page for Davros for his history and a complete listing of all appearances.