The biggest snake to ever exist is the Titanoboa cerrejonensis.
The Titanoboa cerrejonensis is estimated to have been between 42 feet to 47 feet long and weight over a ton.
The massive snake lived during the Paleocene epoch, after the extinction of the non avian dinosaurs.
The largest still living snake in the world is the Green Anaconda which can reach lengths of 19 feet to 20 feet as adults and even weigh as much as 595 lbs.
A green anaconda snake is also known as the giant anaconda snake, emerald anaconda snake, common anaconda snake, common water boa snake or even a southern green anaconda, and is a semi aquatic boa species of snake that is found in South America and the Caribbean island of Trinidad.
The green anaconda snake is the heaviest and largest and second longest snake in the world.
Anacondas including green anacondas are not man eaters by nature and don't usually harm humans unless you get too close to them and they see you as a threat and in that case they can and will bite.
Anacondas including green anaconda snakes will take any prey that they can subdue and swallow and they can also extend their jaws wide enough to get around an adult human's shoulders which is your widest point, so they can potentially prey on people as well.