Zahua: Monk, savannah human, thinker
Zahua is one of the strongest companions you will meet, he has 17 might points. His dexterity and constitution are worth mentioning as well, they are at level 13-14. The other statistics are around 10 points. You will meet him at around 8-10 experience level. At that point he will have a pretty high attack power. However, he will lose health very fast. Think about giving him some light armor or skills that will increase his defense.
You will meet this companion near the Fishery (M1,6) in the Stalwart village. You must walk towards the fish barrel at the western wall of the building. When you try to pull a strange item from the inside, the monk will jump out. After a short conversation you will be able to add him to your party.
Devil of Caroc
Devil of Caroc: Construct, Rogue, Trapper
Devil of Caroc is one of the most interesting companions available in the game. Not only her race is unique - she is a construct, a human soul cursed into mechanical body - but she is also the only rogue that can be added to the party. She has high Perception (16 points), Resolve (15 points) and Might (13 points). She also has many Mechanics and Stealth points. Since the Devil is made of metal, her body is her armor. You can't equip her in any additional armor. The helmet, gauntlet, boots and cloak slots remain active. You should meet her at around 10-11 experience level. At that point she should have many skills focusing on dealing high damage to single enemies. It is wise to combine it with high stealth level for silently eliminating single strong enemies.
The rogue can be met at Galvino side in his office (M8,5) which can be found in the Workshop. To get there, first you must reach Durgan battery, find Galvino cabin (M4,2) there and from there go underground. Now you will have to journey for quite some time through the workshop. It is recommended to stick to the walkthrough for The recluse of the White March quest. Once you find Galvino, you can ask him for permission to add Devil to your party. He will agree if you pay him 700 pieces of gold or if your main character has 12 Perception points.
Devil of Caroc's personal quest is The one that got away. It activates automatically after she joins your party.