Question: What is their first name? | Do  you mean  their  ?can  you  give more  info? | What is the customer first name of the customer with the most number of accounts?
SQL: SELECT T2.customer_first_name  FROM Accounts AS T1 JOIN Customers AS T2 ON T1.customer_id   =   T2.customer_id GROUP BY T1.customer_id ORDER BY count ( * )  DESC LIMIT 1