Get Player Username

I'm trying to create a command that Changes the nbt data of the currently held item.

Ive gotten to the point where everything works except for this line.

EntityPlayer player= sender.getDisplayName();

	@Override
	public void processCommand(ICommandSender sender, String[] args) 
	{
		String output = String.join(" ", args);
		if(args.length == 0)
		{
			throw new CommandException("no name defined");
		}
		else
		{
			EntityPlayer player= sender.getDisplayName();
			ItemStack stack = player.getHeldItem();
			addInformation(stack, player, output);
		}

	}
	
	public void addInformation(ItemStack istack, EntityPlayer player, String itemname) 
	{
		
		NBTTagCompound tag = istack.stackTagCompound;
        
        if (tag == null)
        {
            tag = new NBTTagCompound();
            tag.setTag("display", new NBTTagCompound());
            istack.stackTagCompound = tag;
        }
		
        tag.getTag("display");
        tag.setTag("display", new NBTTagCompound());
		NBTTagCompound tagname = tag.getCompoundTag("display");
		NBTTagList name = new NBTTagList();
		
		name.appendTag(new NBTTagString("§b"+itemname));
		
		tagname.setTag("Name", name);
	}