Cold War is the latest Who instalment penned by Mark Gatiss, and features The Doctor and Clara (Jenna-Louise Coleman) up against an Ice Warrior aboard a Russian submarine.
Dubliner Cunningham - who plays Captain Zhukov - told Access Hollywood that he greatly enjoyed seeing Smith in the role of the Eleventh Doctor.
"Matt Smith is a wonderful Doctor. He's wonderful," Cunningham declared, adding:"He's a very quirky character both in real life and as Doctor Who.
"I'd seriously say, I think he's gonna go down as - definitely one of the classics of the Doctors, definitely, definitely, and a delightful human being - as is Jenna-Louise."(One of the classics?...not under Moffat's writing)
Cunningham is also currently portraying Davos Seaworth in Game of Thrones, which began its third season last weekend in the US and on Sky Atlantic.
Doctor Who airs tonight (Saturday) at 6.00pm on BBC One.
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