Laxman, who always had his finger on the pulse of the nation, died at the age of 94 last evening after suffering multi-organ failure.
Bachchan described him as the "sound of the conscience".
"RK Laxman the silent yet visible sound of the conscience of a nation passes away... Prayer, peace...SILENCE," he posted on twitter with a cartoon of the common man in tears.
"RK Laxman .. In peace and prayer may he rest..,!" Bachchan added.
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"With RK Laxman's demise India has lost it's morning smile," actor Anupam Kher wrote.
Rahul Bose posted, "So very sad to hear of Mr R K Laxman's passing. The quiet chronicler of modern India. He stands alone. My foundation salutes him. RIP"
Laxman was known for immortalising the hapless 'Common Man' with his devastating swipes at politicians but without malice.
"Aam aadmi is grieving today. His creator and voice departed forever. RIP R K LAXMAN," tweeted Manoj Bajpayee