Who revived Strax?

Question

If I remember correctly, Strax dies in "A Good Man Goes to War" but is in a later episode, I believe it's "The Snowmen".

The Doctor says to Clara something along the lines of "He gave his life for a friend of mine", to which Clara replies something like "If he gave his life, how is he here?". Then the Doctor says something like "another friend of his brought him back but that he isn't sure his brain made the return trip".

Is it ever stated in any Doctor Who media (TV, books, guides, etc) who exactly was the one who brought Strax back to life?

Answer 1

Vastra and Jenny.

This is covered in the mini online episode "The Battle of Demons Run: Two Days Later". From the TARDIS Wikia summary:

Strax is woken up by Madame Vastra and Jenny Flint, and is told that he had not died since they had used alien technology to heal his wounds. Jenny says that he had never truly passed away thanks to the resurrection technology and he had been in a state of unconsciousness for two days while the resurrection device healed him. He's angry about not having died. Vastra and Jenny then announce that the station is being evacuated, and they offer to take Strax with them back to London. Strax is hesitant and at first rudely refuses but then changes his mind and agrees to accompany them.