Mertesacker played alongside the forward for club and country and says he is a unique presence.
"Lukas is a great character because he is not only a great football player but he is so positive in everything he does," Mertesacker told Arsenal Player.
“He comes into the dressing every single day having a laugh, every single day he is looking forward to going onto the pitch and smashing that ball into the top corner.
"That's his first idea of the day, whether he's warmed up or not it doesn't matter. His eagerness to do a fantastic job for a football club is in his DNA. I was always amazed by his positivity but as well that he had such a long-lasting career.
"His longevity and his success speaks for itself. Then his responsibility, he played for a lot of clubs and he meant it. His identification with every single club was just a great example.
"His identification with his home, Cologne, is an even better example because he has got so much responsibility there. Lukas is a great character and he has shown the world that he can deliver on every single stage with a positivity that goes beyond my imagination."