In ASP.NET MVC, HTML Helpers are a set of utility methods that generate HTML markup in views. They simplify the process of creating HTML elements by providing methods that generate the necessary markup based on the provided parameters.

While ASP.NET MVC provides a set of built-in HTML Helpers, you can also create your own custom HTML Helpers to generate custom HTML markup. Custom HTML Helpers can be useful when you have repetitive HTML rendering tasks or when you want to encapsulate complex rendering logic into a reusable component.

To create a custom HTML Helper in ASP.NET MVC, you can follow these steps:

1. Create a new static class to hold your custom HTML Helper methods. Let's say the class is named CustomHtmlHelpers. It should be placed in an appropriate namespace.

   using System.Web.Mvc;

   namespace YourNamespace
   {
       public static class CustomHtmlHelpers
       {
           // Your custom HTML Helper methods will go here
       }
   }

1. Define a public static method within the CustomHtmlHelpers class. This method will generate the desired HTML markup. The method should have the following signature:

   public static MvcHtmlString YourCustomHelperName(this HtmlHelper htmlHelper, /* parameters */)
   {
       // Generate HTML markup based on the parameters
       // Return the generated markup as an MvcHtmlString
   }

The htmlHelper parameter represents the current instance of the HtmlHelper class, which allows you to access helper methods and properties provided by the ASP.NET MVC framework.

1. Implement the logic inside your custom HTML Helper method to generate the desired HTML markup. You can use the TagBuilder class to build HTML elements programmatically or use other techniques based on your requirements. Finally, return the generated HTML markup as an MvcHtmlString.

   public static MvcHtmlString CustomButton(this HtmlHelper htmlHelper, string buttonText, string cssClass)
   {
       var buttonTag = new TagBuilder("button");
       buttonTag.InnerHtml = buttonText;
       buttonTag.AddCssClass(cssClass);

       return MvcHtmlString.Create(buttonTag.ToString());
   }

1. To use your custom HTML Helper in a view, you need to include the namespace where your custom HTML Helper class is defined. You can do this by adding a @using directive at the top of your view file.

   @using YourNamespace

1. Now, you can call your custom HTML Helper method within your view by using the Html helper property and the method name you defined. Pass any required parameters to the method.

   @Html.CustomButton("Click me!", "btn btn-primary")

This will generate the HTML markup for a button with the specified text and CSS class.

That's it! You have now created a custom HTML Helper in ASP.NET MVC. You can create additional helper methods within the CustomHtmlHelpers class as needed, and they will be accessible in your views once you include the namespace and call the respective methods.