Is Operator is used to Check the Compatibility of an Object with a given Type and it returns the result as a Boolean.

if(obj is int)
{
 ...
}

As Operator is used for Casting of Object to a given Type or a Class. The as keyword is used to cast nullable types if the specified value is not an instance of the specified type.

AnyClass anyObject = obj as AnyClass;

sometimes in a program we havily use polymorphism and we do not know the actual type of the object , so here for comparison we use IS operator just to check whether the object is of a particular type or not.
As is simply used to convert an object into specific type if the conversion is possible ,where object must be of that type or a child of that type.
The real reason of existance of these two are shorting out polymorphism problems.

The “IS” operator is used to check if the run-time type of an object is compatible with the given type or not, whereas the “AS” operator is used to perform conversion between compatible reference types or nullable types