Russian born, US engineer, Igor Sikorsky , designed and flew the first four engined aircraft in 1913 and designed the first successful helicopter in 1939.
As to why, I can only guess that he saw a need and fulfilled it, or somebody asked him, or he picked up on one of Leonardo Da Vinci's ideas. ( A helicopter design.)
This is the very drawing of Leonardo Di Vinci’s helicopter design that up to this day he must be so humble about!Leonardo da Vinci first to seriously theorize about flying machines - with over 100 drawings that illustrated his theories on flight
Thanks to Mr Igor sikorsky we have aircrafts that have been designed and crafted into a lot of different engineer flighting and things like new modern helicopter and aeroplanes with new and improoved engines!!! And did you that if it wasn’t for the famous painter himself Mr Leonado Da Vinci helicopters might not of been designed for about another 50 years when tecnology was better improoved!!! So thanks!