The Classic monsters, The Sontarans, will be back in Doctor Who Series 4. This information comes from the BBC Doctor Who Site and is therefore confirmed. Christopher Ryan will play a Sontaran Leader in the story which begins filming in a few weeks.
Sontarans come fron the planet Sontar, they first appeared in Doctor Who back in 1973's Doctor Who episode "The Time Warrior".
Here is what the BBC Doctor Who Site have to say;

Christopher Ryan, best known for playing super-cool Mike in the classic comedy series The Young Ones, is set for a guest-starring role in an upcoming Series Four adventure.
Ryan will play a Sontaran leader in the story, due to begin filming in the next few weeks.
"I'm absolutely delighted to be appearing in this new Doctor Who," Chris revealed. "The last time I appeared in Doctor Who was in 1986, Colin Baker was the Doctor and I was still a Young One."
The story in question was the Trial Of A Time Lord, where Chris starred as the slug-like Mentor Kiv alongside Trevor Laird, who played Martha's dad in 2007.
If you know your Who lore, the Sontarans will need no introduction. If you're a newer viewer, however, you may not know that the Sontarans are amongst the greatest villains from the classic series of Doctor Who.
A military, warlike species, able to clone vast armies of themselves, the Sontarans are locked into an eternal struggle with their enemies the Rutans.

For those of you who watched "Eye Of The Gorgon" yesterday, you may have noticed a Sontaran reference. This is great news, can't wait to see them in Doctor Who Series Four, can you?
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