An important part of building a character the PCs never meet is attributes that the characters can see, even if it's indirectly. One idea may be a consistent and vicious manner in which this character ties up loose ends. i.e. Loose ends always end up being fed to a certain ghoul ring in Redmond, loose ends are always missing hands and face.
Note, it is not necessarily the brightest move to have a consistent pattern. The reason to do it is simply story/character. It gives the PCs something they can see, since the character is all but invisible in the game world. Another way they can be seen is through their plots and goals. But if you play the character too intelligent, the PCs may never even see him in this manner. For example, Littlefinger in GOT purposely creates random plots that don't even aid his goals, just in order to confuse enemies.
Consistent subordinates or middlemen is another way. Yet again, it would probaly stretch believability for this type to even have consistent subordinates or middlemen. it's a trade off between letting the PCs see things for entertainment purposes at the expense of making the Johnson a bit dumber than he possibly should be.
The danger with using this type of intelligent character is that if you truly use all your resources to make him intelligent and crafty, the PCs will never even see the character in any manner. It can really feed a GMs ego and give him something to laugh about, but in the end is your goal to entertain yourself or the players? Unlike a novel, in a roleplaying campaign you can't really reveal shadowy plots in cut scenes. (Unless you choose to embrace that style of game, something I have seen done successfully)
So in the end you may have to sacrifice a bit of believability and give him some kind of pattern, if you want the players to at least see the character from the corner of their eyes. Or even make some slip ups eventually out right if you want to give the players the satisfaction of taking down the person eventually. (Or nearly take him down and barely fail)
You can run into a similar danger running secret plots and conspiracies. It has gotten me excited about running my game in the past, but I often was later frustrated by the fact that the PCs never noticed certain things, so in the end a large part of my efforts was known only to myself.