a scientist who devotes himself to doing research
"The investigator spent years analyzing soil samples in hopes of solving the unsolved mystery."
someone who investigates
"The detective worked as an investigator to uncover the truth behind the missing documents."
a police officer who investigates crimes
"The investigator interviewed witnesses at the crime scene to gather evidence."
One who investigates.
"The investigator examined every clue to solve the mystery."
The word entered English in the mid-16th century directly from Latin investigator. It originally referred to someone who searches out or examines something thoroughly.