JSLink Undefined Error

I am customising my List views and other elements with JSLink files.  How do I get data from a column with a space in the name such as "Created by"?  I tried renaming the column to "User" but when I reference it I get "undefined" returned despite the column being selected for the view.

(function () {
    var itemCtx = {};
    itemCtx.Templates = {};
    itemCtx.Templates.Header = "News";
    itemCtx.Templates.Item = ItemOverride;
    itemCtx.Templates.Footer = "</ul></div>";

    itemCtx.BaseViewID = 1;
    itemCtx.ListTemplateType = 100;
    SPClientTemplates.TemplateManager.RegisterTemplateOverrides(itemCtx);

})();

function ItemOverride(ctx) {
    //Renamed Created By Column
    var _userTitle = ctx.CurrentItem.User;    
    var _userID = ctx.CurrentItem.ID;

    return "<li>" +"<span class='announcement-title'>" + _userTitle + "</span>" +"</li>"

    ;}

What am I doing wrong?