They are called SEO executives, Webmasters, Websites optimizers, Digital marketing experts, etc.
SEO executive: He is responsible for increasing the number of visitors or traffic to a website using various SEO tools and strategies.
SEO/SMO analyst: He is responsible for planning and implementing SEO and social media strategies for the clients. He is supposed to quickly understand and support initiatives to achieve the objectives and goals of the client campaigns.
Webmaster: He is responsible for maintaining one or more websites. He ensures that the web servers, software, and hardware are working smoothly.
Digital Marketing Expert: He is responsible for planning and executing digital marketing programs to promote the brand or increase the sales of the products and services of the clients.