Who was the angel at Bethesda that troubled the waters?

This account is in John's gospel chapter 5, verses 2-9. The oldest manuscript records omit verse 4 which identifies an angel as the cause of the water being stirred up. Verse 7 does appear in all the manuscript records in which the invalid man makes reference to the water being stirred up and implies that it is somehow associated with an opportunity for healing.

It should be appropriate to say that it is immaterial who the angel is if scripture does not make mention of the name, and furthermore that there was likely no angel present at all.

In fact, other than this verse, I cannot remember of any reference of an angel being associated with healing. Angels were sent by God to communicate His word or to execute judgment at His command. Never were they to be instruments of mercy, such an action God has left for Himself alone.