WP_Query::is_author() WP 3.1.0

Is the query for an existing author archive page?

If the $author parameter is specified, this function will additionally check if the query is for one of the authors specified.

This is a method of the class: WP_Query

No Hooks.

Return

true/false.

Usage

$WP_Query = new WP_Query();
$var = $WP_Query->is_author( $author );

$author(mixed)

User ID, nickname, nicename, or array of User IDs, nicknames, and nicenames
Default: ''

Code of WP Query::is author: wp-includes/class-wp-query.php ^{WP 5.2}

<?php
public function is_author( $author = '' ) {
	if ( ! $this->is_author ) {
		return false;
	}

	if ( empty( $author ) ) {
		return true;
	}

	$author_obj = $this->get_queried_object();

	$author = array_map( 'strval', (array) $author );

	if ( in_array( (string) $author_obj->ID, $author ) ) {
		return true;
	} elseif ( in_array( $author_obj->nickname, $author ) ) {
		return true;
	} elseif ( in_array( $author_obj->user_nicename, $author ) ) {
		return true;
	}

	return false;
}