In Iron Man (and The Avengers), Tony Stark has created a voice-controlled computer interface called J.A.R.V.I.S. Well, two students from Princeton University have created Jasper, the beginnings of a similar voice-controlled system. You can download the code and install it on your Pi and it will respond to voice commands. It's all open-source so you can adapt it to your requirements. Well worth taking a look! You can visit their website here.