I don't think it's wrong at all even from a common sense perspective when you look at the facts. If you are a company and you are in a lawsuit you are allowed

I don't think it's wrong at all even from a common sense perspective when you look at the facts. If you are a company and you are in a lawsuit you are allowed to call an expert in to defend your position. Companies always choose an expert who is likely to agree with them (as do their opponents!). This guy is an expert in both law and the particular kind of cases. He has also already shown to Samsung that he has a view on the matters that are in line with Samsungs interests. As a judge he comes across as a trustworthy expert. Why not hire him? And for the judge, why not be hired? The case is done, he's not likely to rule between Apple and Samsung again for obvious reasons.