The Three C's: Consternation, Conflict, and Compassion

The moment you give a name to a character, the closer you have come to imparting life to the character and in the process imparting concern for the character's welfare to you.  

Nevertheless, things have a way to go before you are safe; there is the reader to think about as well as the added matter of how your other characters will react to an interloper in their midst or a mere convenience character, brought in like some kick-ass consultant to set things right in the story.

We'll get you back to the reader in a while because readers are important in the long run and because they might well bring things to the table you hadn't even anticipated.  For now, we need to keep you on track--with characters and you.
Some characters are deliberately brought on stage to cause consternation to one or more of the ensemble already in place.  

This consternation might be the source of inconvenience as in an ex lover appearing on the scene or a nearly grown child, returning home on a spring break from school. wanting nothing more than a couch on which to be a potato.  Such characters are in effect armatures around which are wrapped the wires of their ability to produce discomfort and tension in every scene, as well as the aforementioned consternation.  

They might also be brought forth to enhance a conflict already in place or to push beyond the tipping point a tension into conflict.
Although these characters have a specific job description and are accordingly easy to track, we need to remember two vital qualities other than there mere name--they must be presented with some degree of compassion from you, lest their true purpose and, thus, your own motives become transparent.

Begin by imagining the climate and condition in place between the parents of this character in the process by which they selected this character's name.  Yes, I am positing that this new character has parents.

Wait a minute, are you suggesting--?

As a matter of fact, yes; I am.  This exercise has already imparted a sense of social and psychological environments, lathes shaping this character's growth and behavior, quite possibly eliciting a deeper understanding from you, if not outright compassion, relating to who this character is, what this character wants, and what this character is willing to do in order to achieve the goals you have set as a precondition to appearance in this particular story.

To add spice to the stew, you might even consider whether either or both parents wanted this character child, or if this character were an accident at first, then a growing irritant or, perhaps this accident character had come to be much appreciated to the point of becoming what we think of when we think of a spoiled child.

This exercise will provide clues for the next step in the equation--how your new, wanted or unwanted, named character gets along with the rest of the ensemble cast.  Is he or she the kind of emerging nuisance the poet Dylan Thomas became as he moved from university to university and unsuspecting home to unsuspecting home on his now legendary reading tour of America.  Does he or she throw up in the rose garden, borrow large or even minor sums of money without the slightest intention of repaying?  Does he or she come on to husbands, wives, baby sitters, professors' wives/husbands?

What kinds of nerves and wires will your new character cause to fray?  And how, oh, how will you portray this character so that the reader senses you are just as powerless to impede as your front-rank characters and their associates?