In this paper we cluster users of discussion forums into behavioural roles based on features derived from their egocentric reply-graphs. We then analyse the user's popularity with respect to the prototypical behaviour the user demonstrates. We perform this analysis on a selection of discussion forums ("subreddits") from the popular social news aggregation website Reddit.com and show that while many of the forums exhibit similar compositions in user behaviour, different behavioural roles yield

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... fferent distributions of popularity ("karma") among the community. We uncover a small core of highly active users who play an instrumental role in initiating and sustaining communication throughout each community.