Who was the Roman Emperor in time of spartacus?

I believe there was no emperor at the time of Spartacus, as Caesar was the "king." Caesar wasn't actually the king, yet. He was just ruling and decided to become king, until he was unfortunately stabbed twenty three times in the Senate, the day before he left for a five-year war.

There is a link that explains things, if I am incorrect:

http://www.fsmitha.com/h1/ch18.htm