Wondering if in fact there is anything I can do other than move on to another shop.

I'm at a medium size business where there is one engineer who seems to determine their own job title, job description, tasks etc. despite being nominally attached to a team. They are a 'Brent' type - always 'there', always the one swooping in at any hour of the day or night for any crisis or any initiative, leaving nothing for anyone else. At some point Brent's line manager moved on, as did their skip level, so they wound up reporting to a different director with their own wide remit and large number of direct reports rather than a regular EM as would be normal at 'senior' grade. This is despite Brent being nominally a 'senior' rather than lead/staff/principal/manager etc. Brent is very personable and reasonably capable. They get the job done but without being particularly visionary or producing elegant solutions. Brent doesn't really work in a collaborative way or get their work reviewed.

The problem is that Brent seems to actively ensure that they're the only one with administrative access to this and administrative access to that and that nobody else is. Those things are not meaningfully documented and knowledge of and and access to credentials is not shared. This has already had significant consequences to the business including in house systems going down, sometimes for several days, that everyone has to wait for Brent to fix. Naturally the business's incident post mortem system 'could be improved' - boiling down to whatever the incident commander decides is appropriate and the incident commander being decided by whoever wants to grab the job first at the time... Brent seems to be motivated by the intention to be the last one standing when others get laid off- based on things that they have directly said.

Concerns have previously been raised publicly in a 'jokey' way in larger meetings about how the business intends to ensure cover for Brent but it's not obvious that anything has changed in response. Ditto for post mortems - management seem to think 'well the issue was dealt with' (at the time).

Wondering if anyone else has successfully navigated a situation like this and how?