hi. im new. who is blade runner and whats the story line here? (Like the plot i mean.)

In a futuristic society that exists 'early in the 21st century', the Tyrell Corporation has advanced robot evolution to the Nexus phase, creating artificial creatures that are virtually identical to human beings. These "creatures" or replicants have a four year life span and some leave their posts (they are slaves to humans). Blade Runners are highered to track them down and kill or "retire" them.