The Hecatoncheires (Ἑκατόγχειρες) are three giants in Greek mythology. The name Hecatoncheires translates to "hundred-handed ones" or "hundred-handers". They are also called the Centimanes. 
The giants were named Cottus, Briareus (or Aegaeon / Aegaeus) and Gyges (or Gyes) and were the offspring of Uranus and Gaia. The giants were described as having fifty heads and one hundred arms each. [2,3]
The three brothers aided Zeus and the Olympians overthrow the Titans. 
Homers Iliad gave Briareus a second name so that Briareus is the name the gods used and Aegaeon is the names that men used. The name Aegaeon or Aegaeus is sometimes used to refer to Poseidon and in this context the name for Briareus could be patronymic meaning "son of Aegaeus". [5,6]
The most prominent of the brothers is Briareus who is singled out as being good. He is rewarded by Poseidon and is given Cymopolea (Poseidon's daughter) as a wife. [6,7]
The Hecatoncheires in mythology
The various accounts of the giants vary greatly and it is tough to get a unified myth about them.
In the succession myth according to the Theogony they aid Zeus is his fight against Cronus and the other titans. Gaia foretold that the Hecatoncheires would be victorious in battle making Zeus free them in his search for victory. They were instrumental in the Titans defeat and were later placed in Tartarus to guard the Titans. 
This story is however disputed in the ancient lost epic the Titanomachy which was likely written after the Theogony. In this the Hecatoncheires was on the side of the Titans. In this they were not actually hundred-handed giants but instead men living in a city called Hecatoncheiria meaning "Hundred-arm". 
According to Apollodorus the Brothers were the first descendants of Uranus and Gaia dating them older than the Titans. They were unsurpassable in size and might. They were then chained up and cast into Tartarus. When the Titans then overthrew Uranus they freed the Hecatoncheires. 
: George Grote, History of Greece, Volume 12, Harper, 1875, p. 519.
: West 1966, pp. 209–210 on line 149 Κόττος, which says that Cottus was the name of "various Thracian princes"; Bremmer, p. 76; Caldwell, p. 37 on lines 147–153. Kerényi, p. 19, translates Cottus as "the striker".
: Hard, pp. 65–66; Hansen, pp. 159, 231; Gantz, p. 10; Brill's New Pauly, s.v. Hekatoncheires; Tripp, s.v. Hundred-handed pp. 307–308; Grimal, s.v. Hecatoncheires p. 182.
: As her name suggests, see Kirk, p. 95
: West 2002, p. 109 dates the Titanomachy as "late seventh century [BC] at the earliest".