Arsene Wenger made the perfect start to the summer transfer window on Monday by confirming the signing of Schalke 04 left-back Sead Kolasinac.The 23-year-old was hugely impressive in the Bundesliga last team, even making the Team of the Season, making his free transfer seem like an absolute bargain.His arrival means there will now be three left-backs fighting for one spot, with Nacho Monreal and Kieran Gibbs also in contention.What prompted Wenger to sign Kolasinac is the Bosnian's physical attributes and what he has to offer going forward.In 25 league appearances for Schalke last season, Kolasinac notched three goals and five assists - not bad going for someone whose primary job is to defend.He said all the right things in his first interview as an Arsenal player, too, by explaining how his biggest strengths are his mentality and versatility."It feels really good and I'm pleased to be here," Kolasinac told Arsenal.com. "I'm happy to have signed at Arsenal for five years and I'm really pleased."Arsenal has a huge tradition and I followed the club as a young boy, in the days of Jens Lehmann and Thierry Henry.

"Arsenal has always been a club that is well recognised in Europe and I’m pleased to be here.

"I think my main strength is my mentality. I'm a player who will try to help the team as well as I can. My strengths are my mentality.

"There are different positions but I think left-back is where I feel most comfortable. I can play as part of a three at the back too or further forward. I'm really flexible."

Kolasinac may claim his greatest asset is his mentality, but any Bundesliga fan will tell you he was more renowned for his strength and speed in Germany.

A highlights reel has emerged of Kolasinac playing for Schalke last season and, by the looks of it, Arsenal have signed an absolute beast.

The Bosnia international loves a hard challenge and running at opposition players, which is exactly the kind of bravery and steel Arsenal need. Check it out.

SEAD KOLASINAC: BEAST MODE

He's like a mini Incredible Hulk. For years Arsenal have been bullied by their rivals and criticised for being weak, but times are changing.

Shkodran Mustafi and Granit Xhaka were both signed last summer and proved over the course of the season they can handle the physicality of the Premier League.

And it would appear Kolasinac is up to the challenge, too, which is great news for Arsenal fans.