"This is his coat."

Translation: Αυτό είναι το παλτό του.

[Edilvers]

Why is "είναι" necessary here?

Edit: I got it. I was thinking like a Russian. Wow.

[Victoria587638]

Αυτό είναι το μπουφάν του
was marked wrong. I thought μπουφάν is another word for coat.

[RanHinrichs]

I looked up το μτουφάν and το παλτό in Google, https://www.google.com/search?q=%CF%84%CE%BF+%CE%BC%CF%80%CE%BF%CF%85%CF%86%CE%AC%CE%BD+and+%CF%84%CE%BF+%CF%80%CE%B1%CE%BB%CF%84%CF%8C&safe=active&source=lnms&tbm=isch&sa=X&ved=0ahUKEwigyf_j3IrgAhUIxlQKHZtBC5UQ_AUIDigB&biw=958&bih=924. There is no viewable difference between these two words.