I have observed technical people in organizations in the last 30 years who held their boss hostage. These people hoarded technology expertise, avoided documenting their work, spoke inappropriately in meetings and with customers, and still they kept their jobs. I worked with a company years ago where leadership was convinced that one technical person had the power to destroy their business if he ever left. They did eventually go out of business.
With the advance of Agile methods, collaboration, clear roles and sharing of everything drives success. New technical staff are being taught to work this way in their college programs. This has made the old position of technical expert obsolete. There are many examples of people being let go in their later career years with limited opportunities for employment because they are unable to adapt to working with others. To be fair, many leaders never made them. As a leader, be very careful what behavior you tolerate.