Wenger reaches the landmark when the Gunners travel to Premier League leaders Chelsea on Saturday.
Dein, who brought Wenger to North London in 1996, claims that the 64-year-old has revolutionised the way that Arsenal operate on and off the pitch, and is positive that he will leave a lasting legacy at the Emirates Stadium.
"He has transformed the club, revolutionised the club," Dein told reporters. "Whenever he decides to leave he will be leaving behind a phenomenal state-of-the-art training facility, a wonderful stadium, a very good squad which he is trying to improve and a legacy of what he's won.
"Arsene is a football purist. He has a lovely phrase, he calls it 'possession with progression'. Arsene Wenger transformed the club on the pitch and off the pitch. I will go on record as saying he won't be a difficult act to follow, in my opinion it will be an impossible act.
"I would go on record and say I don't think we will see that again in our lifetime. It's a phenomenal milestone; 1,000 games at one club for 18 years. In modern football the longevity in the whole of the 92 professional clubs, you know how long a manager stays in his job for? Eleven months, and Arsene has been there for 1,000 games which is absolutely astonishing."
You can read Sports Mole's feature on Wenger's Arsenal career here.