It always surprises me when I google something that I think should be fairly well known, just because I want to double-check a specific detail for example, and then it turns out there's actually (next to) no content about that thing out there. In this particular case, said "thing" is the bonus boss of master mode Legacy of the Rakata, a flashpoint that has been in the game for about nine years at the time of writing this. So I thought I'd write a quick guide on how to deal with it myself.
I wouldn't say that this is a particularly hard flashpoint boss, but he's not trivially easy either. It's definitely not the type of fight where you can just wing it and hope for the best - you have to understand the boss's abilities and coordinate with the rest of your group.