Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE rental ( first_name VARCHAR, customer_id VARCHAR, rental_date INTEGER )
TABLE: CREATE TABLE customer ( first_name VARCHAR, customer_id VARCHAR, rental_date INTEGER )

### Question ###
What are the first names of customers who have not rented any films after '2005-08-23 02:06:01'?

### Accurate SQL ###

SELECT first_name FROM customer WHERE NOT customer_id IN (SELECT customer_id FROM rental WHERE rental_date > '2005-08-23 02:06:01')