@t octopus, the easiest way to figure out a minifig you don't recognize is to see what looks the most unique, e.g., the torso, the legs... and put in some keywords (like the octan worker, "oil" would have been perfect), then filter down the results by color (blue, in this example), and type (minifig, torso). From there, you can see what minifigs that piece is a part of and find your minifig. :-) That's the easiest way I've found if I have zero clue at all.
Comments
First minifigure:
https://www.brickowl.com/catalog/lego-axel-diver-minifigure-350752
Second minifigure, I think the parts are from different minifigures, the torso belongs to this:
https://www.brickowl.com/catalog/lego-wolf-guy-set-71010-1
Third minifigure (but different face):
https://www.brickowl.com/catalog/lego-city-police-officer-minifigure
Fourth minifigure:
https://www.brickowl.com/catalog/lego-octan-worker-with-blue-shirt-with-small-octan-logo-and-oil-nametag-blue-legs-and-blue-cap-minifigure