The tall Czech striker has found playing time hard to come by during his five year tenure in Rome. Villa have paid a reported fee of £5million for Kozak's services, who hit the net a total of 22 times for the Biancocelesti.
Despite top scoring in last season's Europa League with ten goals, Kozak failed to transfer that form to Serie A. He failed to score in 19 league appearances during the previous campaign, albeit a large number of those came from the substitutes bench. His biggest achievement in a Lazio jersey came when he netted a hat trick during a last 16 Europa League game with VfB Stuttgart back in March.
The 24-year-old has recently forced his way into the international setup and featured in the recent friendly against Hungary. He has scored one goal in four appearances for Michal Bilek's side.
Standing at 6ft 4in, the target man will compete with fellow attackers Christian Benteke, Gabriel Agbonlahor, Andreas Weimann and Nicklas Helenius for a place in Paul Lambert's side.
Kozak started his career at Slezsky FC Opava and has previously had a loan spell at Brescia. He will wear the number 27 shirt.