I don't know who the specific ruler is but it dates to no later than 1352 A.D., which is when the last gold Byzantine coins were made. This link offers a detailed explication of the coinage of the empire: https://www.coins-auctioned.com/learn/coin-articles/ancient-byzantine-coinage. Although it is not clear what ruler the coin belongs to, I see what appears to be a perfect match for the front of your coin in the article.
It is likely an Andronicus II and Michael IX, or Andronicus II and Andronicus III, Byzantium Hyperpyron from 1295 or 1325 respectively
To be honest, it's not a bad quality coin for what it is. The detail is decent. Check out prices on Vcoins and MA-Shops. This sort of coin usually goes for just under $300 US.
I'd say check completed/sold listings on eBay or if you have a nearby coin dealer who is knowledgeable about ancient/medieval coins I'd bring it over and see what he or she has to say.
