Long Story (I hope this is accurate)
Well, there are different kinds of orcs, as you probably guessed.
Orcs were bred in the pits of Utumno from tortured and mangled elves after being captured by Morgoth/Melkor. They split into a number of race strains that survived the chaining of Melkor and spread throughout Middle-Earth.
-Hobgoblins
A pre-Isengard equivalent of Uruk-hai. They are larger than regular orcs and are technically uruks. They were the largest existing orcs before Uruk-hai. They apparently have existed since the orc breedings of Melkor
Quote:
Orc is not an English word. It occurs in one or two places but is usually translated goblin (or hobgoblin for the larger kinds)
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-Preface to the Hobbit
-Uruk-hai
You can probably figure out what these are. Bred by Saruman and Sauron, Uruk-hai are larger, stronger, and fine with sunlight. That is self explanatory. Also called Great Orcs.
Quote:
Great Orcs, that kind is stronger and more fell than all others
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-Half-orcs
Half orcs are supposedly another unsuccessful half-breed of Saruman. Another sunlight resistant breed, half-orcs, or goblin-men, are just another failed experiment, present only at the Battle of Helm's Deep where they were all killed by Huorns.
Quote:
But these creatures of Isengard, these half-orcs and goblin-men that the foul craft of Saruman has bred, they will not quail at the sun
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-TTT, Helm's Deep
-Olag-hai
Not often mentioned, but particularly strong. These were bred during the War of the Ring, a mix of troll and uruk. They were larger and stronger (the strongest orcs in existence), but far stupider.
-Snaga
Regular orcs, but lesser. These were probably Melkor's strain, now in the service of Sauron. They were slaves and cannon fodder, but there were many of them.