There's Always One
Sometimes there's two or even more!
About Those Who Monopolize Threads
A group member who wants to monopolize a group is soon recognized These are the ones that 'know' everything and post to let us know they are smarter than we are, even when some of the answers they give are suspect sometimes and just down right wrong at other times.
They monopolize conversation threads and post very long messages, telling us more than we want to know. They can be argumentative and often condescending. Some folks will call these members 'trolls' although they may not be trolls, just attention grabbers. A few actually want to help, but sometimes their 'help' can get to the point of being a turn off. It's evident they want the last word.
The unfortunate aspect of such members is the fact they may eventually alienate the membership in general and will lose the ability to help even though they may be qualified to provide real help.
About Trolls
These folks will come and go in groups. They often will join with a new ID and try to pretend they are really needing help. They will ask ridiculous questions (for them, they know better!) and then may challenge the responses with such things as 'How do I do that' or 'That didn't work'. Some trolls have so many identities they can't keep up with them. Savvy owners/moderators soon learn who they are. They may be removed and banned; or maybe they are left in the Group so they can be watched.
Eventually a troll will move on if the desired actions don't materialize for them.
'Do It My Way', or the Needy
The really needy members may be a combination of monopolizing and being a troll. Most of us don't understand what makes these folks tick, we just want them to be quiet and/or go away.
For want of a better description than 'needy', these are the members who want to tell the group owners/moderators how to run their group. This can consist of telling us what the rules should be or even telling us to remove other members because they don't like answers provided by those members.
These folks just want to be in charge. They need to get their own group.