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Dramas in which guy hides his true identity Or
Has multiple identity,  Or Pretending he's Bad Or Pretending he's Poor Or Pretending he's Gay.
Thank you & SarangaeO in advance :) 
Watched
1. School 2017
2. School 2013
3. Healer
4. Innocent Man
5. City Hunter
6. Kill me heal me
7. Hi my sweetheart
8. Cheese in the trap
9. Ruler: Master of the Mask
10. The King Loves
11. You Who Came from the Stars
12. Blood
13. Personal Taste
14. Lookout/The Guardian
15. High School King of Savvy
16. A Love to kill
17. Me too, Flower
18. Neighborhood Hero
Hides his identity:
Please Come Back, Mister
Mr. Back
My Boss, My Hero
You Who Came from the Stars
Can You Hear My Heart
Prince William

Pretending he's bad:
Just You
Bride of the Century
Devil Beside You

Multiple identity:
Secret Garden (swap bodies)
49 (swap bodies)
Hyde, Jekyll, Me
Dong Yi: king pretends he's a justice officer 
Thank you guys for your recommendations . Watched Devil Beside You, absolutely loved it :) Currently watching white Christmas ... I am gonna be very busy for few days :) Thanks a lot guys.
The Bridal Mask
That Winter, The Wind Blows
The Incarnation of Money
Wannueng Jaa Pben Superstar(pretending he's gay)
Secretly, Greatly(movie)

Thank you Guys. Watched all of 'em. :) 
Currently watching Cambrian Period (2017).

More recommendations Please.  

Cheongdamdong Alice

Maou

I'm Sorry, I love you

Hwarang

Kaitou Tantei Yamaneko

Kazoku Game

Orthros no Inu

Suna no Utsuwa (2004)

Taiyou no Kisetsu

The Liar and his Lover

Easy Fortune Happy Life (Taiwan) (Not exactly what you want,Pretending to be good and in love with the female)

Haeundae lovers(Hide his identity)

Lady and the liar (China)(He pretends that he is the female's fiance, because she lost her memory)

Legend of Lu Zhen (China) (almost Like Dong yi- He is crown prince but pretends that he is just a bodyguard )

Pin anong (Thailand) (He pretends he is just a worker not the owner of the farm)



tunnel (2017)
oh my ghostess
Gu family book
Hit the Top
Iljimae
Kurosagi
reLIFE
Rebel: Thief Who Stole the People
the beauty inside
reunited worlds
yong pal

Love in the Moonlight / Moonlight Drawn by Clouds

Love O2O (c drama)

The Masked Lover (t drama)