Tosun's arrival answers manager Sam Allardyce's desire for a striker who will add pace, goals and physical presence to the Everton forward line. Allardyce had recently talked up the Toffees' need for more firepower, noting how finding a prove goalscorer is "the hardest job of all," per David Maddock of the Daily Mirror.
Goals have been something Tosun has dealt in all season for the Black Eagles. The 26-year-old has scored 14 times across all competitions, helping Besiktas qualify for the last 16 of the UEFA Champions League in the process.
The fact Tosun has been content to turn his back on playing in the knockout phase of Europe's premier club competition underlines the financial and sporting lure of the Premier League.
For their part, Besiktas have been happy to indulge his desire to move on during the season. Club president Fikret Orman revealed the Black Eagles are already "working on a replacement," per Paul Joyce of The Times.
Tosun will know how his quickness, instincts and versatility will set him apart in an Everton squad lacking match-winners up top. Oumar Niasse and Dominic Calvert-Lewin have struggled to lead the line, while 20-year-old Nikola Vlasic and former Malaga star Sandro Ramirez are better suited in wide areas.
Allardyce will count on Tosun to be the focal point of his team's attack, with his pace and the vision of Wayne Rooney a potentially potent combination.