Dorothy f. Greek δῶρον 'gift' + Greek θεός 'god'.
The name of two 4th C virgin martyrs, a 14th C Prussian saint, a 15th C queen consort of Denmark, Norway, and Sweden, a 15th C queen consort of Bosnia, and two 16th C queens consort of Denmark and Norway.
Cf. Theodora, of identical etymology. The name did not become common in England until the 16th C.