The mind may need a little preparation for the term "Troll lawyer". Vampires, obviously; Dwarfs are argumentative and much inclined to strict rules; there is a well-known Zombie, but a Troll with an argument more sophisticated than a club? Well, Mr Thunderbolt is not the average Troll. He's the nephew of the Diamond King and diamond himself. He has articled at Morecombe, Slant and Honeyplace and is even accredited in the court of the Low King.
While his uncle is pure diamond, Mr Thunderbolt has a mere sparkle to his rock to indicate that he is "diamond through and through", and may therefore be looked at directly without risk of blindness.
Being diamond prevents him from telling lies, a seemingly fatal disadvantage in his profession, but he's apparently clever enough to overcome even this. He is so reliably honest that he is trusted to represent both parties in the partnership of Harry King and Dick Simnel.