If you want to express that someone is in control or in charge, the term "in command" is good to use. However, there are many synonyms you could use to vary your language and sound more expressive. For instance, "in power" means that the person or entity has authority and influence. Another word is "in charge," which implies that the person is responsible for managing something or someone. You could also use the phrase "in control" to describe someone who's leading, regulating, or managing something. Lastly, "in authority" means that person has power and jurisdiction over a particular area or activity. By utilizing these synonyms, you can make your writing more engaging and diverse.