Someone who buys significant shares of a company and leverages them to convince a coalition of other investors to demand changes.

You think a company could make better decisions, so you buy a large (but not controlling) chunk of shares. With a relatively large chunk of shares, you can then start making demands from the board and hope that other shareholders bandwagon behind you. Ideally stock price goes up as a result and then people sell higher than they bought for.

Basically people who believe they have all the answers to running a successful business, yet don’t feel the need to apply that towards just running a successful business themselves.

Or the origins of the lost mines of Moria.