>>What kind of special skill we are talking about ?
>
>I won't get too specific, but it is fixing a very expensive and uncommon type of medical device. He is good at fixing it. But I (and everyone) is convinced that he purposely pushed other people away with anti-social behaviour so that he could become the sole expert.

I've come across a few of these "sole expert" types in my time. I must say most were very amiable. Proud of their expertise and happy to show it off.
One or two, though, did seem to take steps to ensure they remained the only one capable. I see two possible solutions:
1) Find out if there's some replacement for the equipment that either comes with a repair service or is cheap enough not to be worth repairing. My bet is that there is.
2) Get a second one of the units so that down time is more palatable, then learn how to fix it yourself and let the boss know.

Does the equipment in question break regularly? If so, it sounds like a replacement would be a good idea anyway.
Didn't you say earlier that the guy's been working from home?... Does he take the equipment home too? Or does it break only infrequently, so he is doing other work from home?

But, frankly, your simplest and most productive course of action would be to simply IGNORE THE GUY. Shun him like he is the plague. Just always be too busy to talk to him, no matter what it is that he needs/wants.



>
>>Are you sure it is only skill that keeps him (them) on top or they are
>>blood related to top management?
>
>Yes. No blood relation since this is not allowed in the organization.
>
>>From the other side it is actually missmanaged situation. What if he
>>is permanently away for any reason ?
>
>My opinion is that would could rely the the company that sold us the equip to fix it. Other places pay for this. We then could train someone (if they did it full time) within 3-6 months to get to his level.
>
>>What is gonna happen ?
>>If that skill is so mission criticall, then managment should by all means find the way to educate more people to be able to perform the same.
>
>Exactly and this is normal operating procedure in our dept.