People who have done very good things, but have not received praise (see RewardReputation). This can be a positive thing: sometimes there are heroes that prefer to remain unsung, and if they were lauded with praise would retreat from those actions that brings praise, and thus the community is poorer for it. This is a good reason to allow anonymous actions, because not everyone wants to be a KarmaWhore. See also: Wiki:PleaseNoCheerleading
However, this can also be a negative outcome, where some AttentionSeeker has contributed good work, but is not being given the rewards they deserve or desire. Such UnsungHeros frequently depart to other communities where their talents are better appreciated, leaving those behind to wonder why everything has suddenly collapsed. Some forms:
In the first two cases, the hero may eventually give in to pride. Such reluctant heros are not reluctant to act heroically, but are reluctant to accept all the consequences and requirements of being regarded as a hero. Ideally, seek ways to praise such heros without forcing them to accept these unwelcome consequences. For example, give generalised praise to your anonymous contributors, and seek out heros who haven't been given enough recognition.
In the second two cases, the problem is very much with the community, which is failing to appropriately support its members. A TechnologySolution can help to some extent, and features such as "karma" and "xp" and "mojo" attempt to automatically provide positive feedback. However, these features have disadvantages, and the best solution may be for community leaders to ModelDesiredBehavior.