The aim of each & every employee should be to become a valuable asset to the company.
OR a most valuable employee-MVE just like some sportspersons are known as most valuable players of the sports season.
A most valuable employee is the one who is able to contribute in the most significant way to the success of a team & the organisation.
Even though no one is indispensable, companies go great lengths to retain, promote & encourage MVE who make strategic contributions to the growth of a company.