Karan, the son of acclaimed producer Yash Johar, made his directorial debut with "Kuch Kuch Hota Hai". He also directed films like "Kabhi Khushi Kabhie Gham..." and "Kabhi Alvida Naa Kehna". Karan's counter-terrorism drama "My Name Is Khan" was appreciated by critics and audiences alike.
Earlier this year, Karan became a father to twins via surrogacy.
Here's what the celebs had to say:
Shabana Azmi: Karan Johar salgirah mubarak (happy birthday) Karan jeete raho khush raho (Live long and stay happy).
Anil Kapoor: Happy Birthday to the new father on the block! Karan Johar! This year has already been amazing for you and I hope the rest of it is as well!
Varun Dhawan: Happy birthday Karan Johar. Wish you many more smiles ahead. You are the best person I know. Thank you for being you.
Alia Bhatt: Happy Birthday to my most favourite person in the whole world! Karan Johar you're my friend, my father, my teacher and last but not least, you're my in-house fashion police (the only one that matters). I don't know what I'd do without you! Love you Karan.
Farah Khan: Happiest birthday Karan Johar! May the pouts always be full my friend! Love you.
Rajkummar Rao: A very happy birthday Karan Johar sir. Sending you loads of love and wishes. More power to you.
Abhishek Bachchan: Happy birthday Karan Johar. Thank you for all that you are and for the amount of love you give and spread. Have the best year. Lots of love.
Nimrat Kaur: Happy happy birthday Karan Johar. There's no one quite like you and that only gets better with time! Celebrating you now and always.
Huma Qureshi: Happy birthday Karan Johar to the sweetest most loving new dad on the block...loads of hugs and kisses.
Vishal Dadlani: To one of the kindest, bravest, most hilariously and brutally insightful people ever! Happy Birthday Karan Johar! Have another stellar year!
Bipasha Basu: Happy Birthday Karan Johar. Wish you an amazing year filled with more of all the wonderful things in the world.
(With IANS Inputs)