I bought this coin because the obverse picture looked like a movie or TV space alien.
And not a nice one!

Details:

Byzantine Justinian (AD 527-565) AE Follis

Obverse: Diademed, draped, and cuirassed bust right
D N IVSTINIANVS PP AVG
Reverse: Large letter "M"
Small star left, cross top and right, gamma under "M"
Exergue: CON (Constantinople mint)

Catalog: Sear 158 - Struck AD 527-538 - Size 30mm

Note: The "M" is a Greek letter for the number 40.
Note: Value 40 nummi. Gamma is the mint officina letter.

Full name: Flavius Petrus Sabbatius Iustinianus
Life span: AD 482-565