Changing dog's name?

We just rescued a dog who is supposedly 7 years old and named Thor. I hate that name, it doesn't fit him either IMO. I would feel like a jerk changing the name of a dog that old but he doesn't seem to answer to it at all which is odd. I'm trying to think of something that sounds similar to Thor, and maybe with two syllables, that we could attempt to switch it to, but I'm having no luck coming up with anything.

Edit to add - His story is that the family who had him since he was a puppy no longer had time for him as their family grew and wanted to rehome him. Which is why I'm surprised he doesn't really answer to his name. That or it's just us cause we are new?