The Toffees have wasted no time in enhancing their squad this summer with Jordan Pickford and Klaassen already signed up as Koeman looks to keep moving in the right direction next season.
Klaassen, who captained Ajax for two seasons, arrives on Merseyside for a fee of £23.6milllion and has agreed a five-year contract.
The 24-year-old is a product of the famous Ajax academy and made 163 appearances for the Dutch giants, scoring 49 times and winning three Eredivisie titles.
Koeman feels Klaassen’s hardworking attitude will help him to settle quickly with Everton and has hailed his leadership qualities.
"He is a player who is only 24 but has a lot of experience and is a leader on the pitch. He has already captained Ajax for two seasons and that shows you the type of person he is,” Koeman said.
"He is hardworking, likes to press and, of course, will give us more creativity and goals."
Everton will be attempting to fight on a number of fronts next season and punters using their free bet may want to back the Toffees to mount a serious challenge for a spot in the top-four next term.