I think very few readers will identify the gentleman to the left from this unusually unflattering bust. Other busts and images we see of this emperor are much more flattering than the one we see here.
I will give you a small verbal clue. The Roman Senate officially sanctified him as one of the Roman deities not long after his demise. I will give credit to the first reader to respond with the proper answer. Thank you and God Bless.. Jerry..