Unable to retrieve User data from Parse database with query

I'm unable to retrieve any user data from the parse database with two query methods. I can get all currentUser data quite easily; however, can't seem to successfully retrieve data from other users. I have a feeling it's quite a simple fix that I'm looking over but I've tinkered with my code for a while now and still returning nil for each variable.

First query method:

let userQuery = PFQuery(className: "User")
       userQuery.whereKey("username", equalTo: username)
   userQuery.findObjectsInBackgroundWithBlock { (users, error) -> Void in
      if error == nil {
        if let objects = users {
            for object in objects {
                if let user = object as? PFUser {

                    self.userBio = user.objectForKey("bio") as! String
                    if user.objectForKey("icon") != nil {
                        self.userIcon = user.objectForKey("icon") as! PFFile
                    }
                    if user.objectForKey("header") != nil {
                    self.headerFile = user.objectForKey("header") as! PFFile
                    }
            }
        }
    }
    }
}

Second query method:

let userQuery = PFUser.query()
       userQuery?.whereKey("username", equalTo: username)
   userQuery!.findObjectsInBackgroundWithBlock { (users, error) -> Void in
      if error == nil {
        if let objects = users {
            for object in objects {
                if let user = object as? PFUser {

                    self.userBio = user.objectForKey("bio") as! String
                    if user.objectForKey("icon") != nil {
                        self.userIcon = user.objectForKey("icon") as! PFFile
                    }
                    if user.objectForKey("header") != nil {
                    self.headerFile = user.objectForKey("header") as! PFFile
                    }
            }
        }
    }
    }
}

Thanks in advance for any help!

let userQuery = PFQuery(className: "User")

needs to be changed into

let userQuery = PFQuery(className: "_User")

since the user class of Parse.com is a special class. and it's name is by default spelled with an underscore.