I can only think of the definition of the General Data Protection Regulation (GDPR) of

'controllers, processors, joint controllers'

Check EU GPDR - Definitions

http://www.privacy-regulation.eu/en/article-4-definitions-GD...

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Note added at 1 hr (2018-08-13 12:59:47 GMT)
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Maybe, it is joint controllers, depending on the context.

This is not a data protection term as such.

"Prescriptores" are people who recommend a company's services to others. They are sometimes called "prescribers" in English, though this term is not very widely used. "Influencers" is very similar, but there's a slight difference, because influencers (a big phenomenon on social media now) are people whose recommendation has marketing value because they're famous, or at least well known: people have heard of them. But "prescriptores" are not necessarily like that; they're simply people who spread the word and have some sort of beneficial agreement with the company.

I think this falls into the category of what's known as word-of-mouth (WOM) marketing: that's what "prescription" in this sense refers to, and people who do it are called word-of-mouth agents.

"Word-of-mouth marketing (WOMM, WOM marketing), also called word of mouth advertising, differs from naturally occurring word of mouth, in that it is actively influenced or encouraged by organizations (e.g. 'seeding' a message in a networks rewarding regular consumers to engage in WOM, employing WOM 'agents')."
https://en.wikipedia.org/wiki/Word-of-mouth_marketing

"Prescriptores
BOCA - OREJA"
http://www.sanperhouse.com/prescriptores/

"3. La importancia del boca-oreja
Según el estudio ““El comportamiento del consumidor online“, entre el 49 y el 62% de los internautas practican la recomendación o WOM (Word of Mouth). Así, los seguidores en las redes sociales son prescriptores: tienen la capacidad de conectarse e influenciar a nuevas audiencias."
https://www.iurisdoc.com/es/influencers-culturales-8-claves-...

"Mobilize your Word-of-Mouth agents. All you have to do is mobilize your advocates and encourage them to engage in your Word-Of-Mouth marketing campaign."
https://www.postspeaker.com/word-of-mouth.html

¿Es la figura del broker hipotecario el "hombre del saco" para la ...
https://futurfinances.com/es-la-figura-del-broker-hipotecari...
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Dec 12, 2008 - El canal prescriptor, bien diseñado, es un buen canal. El problema es que hay que seleccionar al broker con criterios de profesionalidad y ...
La Importancia de los Brokers como prescriptores para las Entidades ...
growfinancial.com.co/brokers/
Mar 19, 2018 - Las entidades financieras han visto una oportunidad muy importante al tener como aliados estratégicos a Brokers o prescriptores, los cuales ..

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Note added at 1 hr (2018-08-13 13:30:27 GMT)
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Prescriptor has a variety of meanings, but the context you have provided shows that in this case the job involves working in collaboration with a bank to provide solutions to the borrowing requirements of third parties (requerimientos de deuda por terceros), so this is the only meaning that fits.

Política de Ejecución y Gestión de Órdenes - GPM Broker
https://www.gpmbroker.com/.../Politica.de.ejecucion.y.gestio...
Dec 1, 2016 - centro de ejecución específico y los corretajes del bróker ... o Saxo Bank, de las cuales GPM es “introducing bróker” o prescriptor, para la.