There are many species of Horse Fly in different genera. Many are large with colourful or patterned compound eyes. One thing they all have in common - the female needs blood in order to make her eggs, like the Mosquito, and she bites - like the Mosquito but a lot more painful. Some species prefer horses, cattle or deer but most will take human blood if available. The male doesn't bite.
The Common Horse Fly (also Horsefly) above, also called a Cleg Fly and specifically the Notch-horned Cleg Fly, Haematopota pluvialis, has attractive, patterned brown wings and red, striped eyes.
Deerfly, Chrysops relictus, called the Twin-lobbed Deerfly to distinguish from other Chrysops Deerflies, is large with bright green, patterned eyes, patterned wings and black markings on fawn.
Another common Horsefly is the Banded-eyed Brown Horsefly, Tabanus bromius, above, with big, green-brown compound eyes (red bands close-up), clear wings and dark brown markings on fawn.
(A better candidate to be called "Notch-horned.")
Another Horsefly - yet to be identified.