What is the role of WebDriver in Selenium?

Selenium WebDriver is a key component of the Selenium suite which is used for automated testing of web applications. It is an open-source API that allows developers to interact directly with the web browser. WebDriver uses a different underlying framework from Selenium's JavaScript Selenium-Core. It provides better support for modern advanced web-app testing problems.

WebDriver makes direct calls to the browser using each browser’s native support for automation. This allows for more realistic, reliable, and faster automation of browser activities, making it a preferred choice for web application testing.

Main Roles of WebDriver in Selenium:

1. Browser Control: WebDriver can simulate the behavior of a real user by controlling actions performed in the browser. It can input text, click buttons, select checkboxes, submit forms, navigate between pages, handle popups, and so on.

2. Interaction with Web Elements: WebDriver can find and interact with web elements. It provides methods to locate elements by their HTML properties (like id, class, name, etc.) and perform actions on them.

3. Handling of Alerts, Popups, and Windows: WebDriver can handle different types of alerts and popups (like JavaScript alerts or file download popups). It can also switch between multiple windows or iframes.

4. Synchronization: WebDriver provides implicit and explicit waits to handle synchronization issues.

5. Page Navigation: WebDriver provides commands to navigate forward or backward in browser history, to refresh the current page, or to navigate to a new URL.

Here is a Python example of using WebDriver with Selenium:

from selenium import webdriver

# Create a new instance of the Firefox driver
driver = webdriver.Firefox()

# Go to a webpage
driver.get("http://www.google.com")

# Find the search box element by its name
search_box = driver.find_element_by_name("q")

# Type in the search
search_box.send_keys("WebDriver")

# Submit the form (this will start the search)
search_box.submit()

# Close the browser
driver.quit()

In this example, Selenium WebDriver opens Firefox, goes to Google's homepage, finds the search box, searches for "WebDriver", and then closes the browser.

Remember that WebDriver supports multiple programming languages (Python, Java, C#, Ruby, JavaScript) and multiple browsers (Chrome, Firefox, Safari, Edge, etc.).