When I last checked (which was 5th edition), units of Trolls could be lead by Heroes and Characters yes
As for the current edition (I think Warhammer is up to 8th now?) I haven't a clue but would assume it's still ok
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~The ravings of a single mad Goblin is bad enough, but such a power-hungry, malice-filled creature as Mortis can never hope to be understood~