Declaring an entity

I have
Player player = event.getPlayer();
int fx = 61;
int fy = 65;
int fz = -1040;
World world = Bukkit.getWorld("Lobby");
Location Zombie = new Location(world, fx, fy, fz);
Entity Bill = player.getWorld().spawnEntity(Zombie, EntityType.ZOMBIE);
((LivingEntity)Bill).setCustomName(ChatColor.BOLD + "" + ChatColor.RED + "Bill");
((LivingEntity)Bill).setCustomNameVisible(true);
if (event.getRightClicked().getPassenger() == Bill){
but how would I make it so it doesnt create a new zombie. How would I declare a zombie with that instead of having to create Bill each time. Cant I just declare bill.

 

Your question is a bit vague.
Do you want to use an existing zombie?
You can get a right clicked entity in PlayerInteractEvent for example.
Then check if the right clicked entity is a living entity and if so, cast it to LivingEntity.
Then you can apply your changes.

But there are also other ways of getting mobs.