How do I resurrect essential NPCs in Skyrim?

I was having some problems in Whiterun with the guard because I needed to pay a fine of over 3000 gold (a considerable quantity for someone that just started the game), so I decided to kill all the guards. The problem came when Commander Caius (an essential NPC) started to attack me, so I attacked him too.

As essential NPCs cannot die, I decided to used the console to set him to be mortal. After that I killed him.

Some of my friends told me that this Caius is an important character in the game, so I want to resurrect him. I still have his corpse, if it's needed.

Is there any console command that can be used to resurrect someone?

Thanks.