In English, we use "to become" or "to get" for almost any change in state. In Spanish, the verb you choose depends heavily on how the change happens.
Voluntary and gradual changes with hacerse
Use hacerse (literally "to make oneself") for changes that involve personal effort, such as a profession, or changes that happen gradually over time. It is the go-to verb when someone or something slowly develops a new status or reality.
| She became a specialist at the clinic. | Ella se hizo especialista en la clínica. |
| The computer became indispensable for the project. | La computadora se hizo indispensable para el proyecto. |
| They became allies during the war. | Ellos se hicieron aliados durante la guerra. |
Deep or sudden shifts with volverse
Use volverse for deeper, often involuntary changes, especially regarding someone's personality, character, or behavior. It implies a more intense shift, such as becoming bitter, obsessive, or insensitive.
| The boss became very bitter because he failed. | El jefe se volvió muy amargado porque fracasó. |
| The detective became obsessive about the case. | El detective se volvió obsesivo con el caso. |
Lasting results and physical reactions with quedarse
Use quedarse (literally "to stay" or "to remain") to express the state someone or something is "left in" as the result of a specific event. It is commonly used for physical changes, permanent losses (like going bald or becoming widowed), and strong immediate reactions (like being left motionless or perplexed).
| My grandfather became a widower last year. | Mi abuelo se quedó viudo el año pasado. |
| He had already gone bald before the wedding. | Él ya se había quedado calvo antes de la boda. |
| The ally was left perplexed upon hearing the plan. | El aliado se quedó perplejo al escuchar el plan. |