indispensable - essential
If somebody or something is described as ‘indispensable’, they are so important that it would be difficult or impossible to manage or function without them. It tends to be used more frequently in a professional environment.
I gave Jane a raise to keep her at the company. She is an indispensable asset to me.
Robert’s indispensability to these negotiations is due to the respect he commands from both parties.
I question the perceived indispensableness of the new software. I believe we could operate just as successfully without it.