When looking at different monsters of the medieval times the first monsters we come into contact with are Giants in The History of The Kings of Britain when Brutus's men are attacked by them. We also see Arthur defeat a giant on Mont Saint Michel all by his lonesome self. We always see that the giants aren't portrayed as very bright, they generally fight with their fists or with clubs and in this battle we are told Arthur is victorious with his sword.
In the travels of Sir John Mandeville giants are 28 or 30 feet tall and they don't wear clothes, but they do wear the skins of beast which they clothe their entire bodies in. They eat raw flesh and drink milk, but don't eat bread, they don't live in houses and they will gladly eat a human at the drop of a dime. We also hear of another isle that has giants of ups to 60 feet tall, but no man lives to tell the tale because if they were to go there they would surely be eaten.
In today's modern monsters we see giants not portrayed in this evil, deranged, cannibalistic way. In fact the jolly green giant on the vegetable bags doesn't tend to kill people, J.K. Rowling wrote a half giant into her story of Harry Potter by the name of Hagrid and he's one of the most beloved characters who wouldn't hurt a fly if he didn't have to. I mean let's look at his track record with fluffy, Buckbeat, Norbert, Harry, etc.
Another monster very similar to the giant is the troll. They could be seen as large evil creatures and were sometimes connected with demons and hell. A lot of medieval tales parallel trolls with bridges. In The Faerie Queen, King Arthur who we see as the symbol of a Christian knight, defeats a giant troll, who in that case represents evil. The most known tale of trolls and bridges is the tale of the three billy goats gruff. In Norse traditions they used the term Troll to describe hostile giants. In some tales they are able to be seen as being capable of working black magic but in most tales giants and trolls, pretty high on the enemy list for humans.
Take Harry Potter for example, someone lets a troll in and it's this big dumb giant thing carrying around a club that almost takes out Hermione, and if Ron Harry weren't there to save her she could of been dinner.
Interestingly enough I did read that trolls don't do so well outside in the sun, and they can be dim-witted and and confused so you're best bet to survive a troll is to get them in direct sunlight.