Artist’s depiction of a famous experiment. Which experiment? Who the dude in the painting?

Cracked by: rohanquizzer, raklodramA, Rogi, finkle, tanwi, rickde, Sumanth Patlolla, Amarendra Kumar, Anjul, Vishwas B Sharma, Kaustubh Mhatre, KK, Thejas V R, shrik, Mr.Bay Leaf, Bharath, jowens, Rahulk, Manish Achuth, Ananth, Dibyo, vinayaknp, Raghuvansh, v.chandrashekar and nandha k samy