the_category_head( string $before = '', string $after = '' )

Source

File: wp-includes/deprecated.php

function the_category_head( $before = '', $after = '' ) {
	global $currentcat, $previouscat;

	_deprecated_function( __FUNCTION__, '0.71', 'get_the_category_by_ID()' );

	// Grab the first cat in the list.
	$categories = get_the_category();
	$currentcat = $categories[0]->category_id;
	if ( $currentcat != $previouscat ) {
		echo $before;
		echo get_the_category_by_ID($currentcat);
		echo $after;
		$previouscat = $currentcat;
	}
}