If i had an IE as one of my player characters, the player would not know, or he'd be a "true" IE and be powerfull enought to assume his background.
There is nothing worse than having NPC with awesome power because of their background, but the moment it is a PC, the "boost" in power becomes something lame as "+1 to resist toxins, +1 dice for magic" ...
Having a very powerfull character ran by a player is very hard to deal with. I mean VERY hard.
You cannot be behind the player all the time, and tell him everything he must do.
The player must have extensive knowledge about all subject the PC is supposed to have.
The player must realise his implications in the world, and that all his actions will have reactions accodingly. Politics will play a major part in his role. The PC must have clear objectives, that drives him so that you as a GM know where the PC is going, and that the player have a direction to follow not to get lost and start playing "god".
One very important thing to do is to give the PC a "Patron", or lets just call it a Boss. The characte isnt free : he has responsabilities, a cause (he is not here to get the nuyen), and has a boss, much more powerfull than him that gives him directions and orders.
Lets take an exemple on how to deal with an IE PC in a classical run :
The players have done the first story in Harlequin. The IE joins them for their next run that has nothing to do with Harlequin. He poses as a Physad/Mage or whatever ... and just want to be part of the team and earn the other PC's trust.
The IE is sent by Alachia or some other very powerfull IE to find out about who's bugging Erhan, or even she knows what's happening and want to have a secret hand in the affair : help Harlequin or Erhan depending on the outcome ...
The player is member of the Song Birds, and so has pledge an oath of secrecy to Alachia. This means massive gesa, ritual magic etc ... if he breaks it ... well he doesnt want to know what will happen, but lets say he knows there wont be any place to hide from her, if of course he's still alive.
The player must secretly report to her mistress, sometimes he'll have to do some kind of secret counter-mission during the run, but most importantly he must not be discovered by the other players.
As time passes, the other players should start having doubts about the IE. In order not to frustrate them, you need to give them somethng (and by that i'm not saying karma or nuyens).
For exemple, make one of the PC meet some very important NPC, and give secret informations to the player, giving him hints about the IE.
That way the IE player will be surprised to know when the mask falls that some other players will have intel on him.
The PC(s) that had secret informations will be pleased to have special contacts and secret meetings. When the mask falls they'll be proud to be the one bringing whatever information they gained, and that way they will forget about the fact that one of the other players has like 10 times his build points (if not more).
The players that dont gain information or "special" contacts, need to have something too. Even some bad stuff (i always consider that it's better to have bad stuff happening to your character than nothing at all).
Make him the center of the next story for some reason or another.
This of course is an exemple, and applies to most games when you have a very powerfull PC.
To sum up my opinion, in order to be successfull in master such a PC you need :
- The PC needs strong guidance before the game starts.
- The PC must have a "boss" more powerfull than himself
- The Player must realise all his responsabilities, and be fully aware of the consequences of his actions.(the GM must not hesitate to tell directly to the player "if you fuck up, the game is ruined")
- The PC must be in the story for a good reason, he must have clear objectives.
- Part of the other PCs must be progressively in the confidence and must play an active role in the story.
- All other PCs must have some sort of compensation to overcome any "jalousy" issues. That compensation must not be obvious and must not feel like "here's your bone to gnaw, now STFU and play"
That later part must not be overlooked, even with mature players, this can lead to serious problems.
My two nuyens on the subject