They have almost no IQ, with their Chieftains being elected because they are the stupidest in the tribe, and the Brutes decisions are based on which option will almost certainly end in failure. They do not have individual names because they are so stupid, and they can't use proper Covenant weapons, they had to have special ones made just for them. The Brutes are now extinct after the Elites, as well as quite a few willing League races, glassed their homeworld of Dosiac. This is why there are no Brute Members of the League. The last Brute to be a League Member was Tartarus, The Supreme Monkey, but he was killed by the Arbiter.Brutes have a pack mentality, which means that each individual Brute contributes its meagre IQ to the pack to create a combined IQ for the whole group. The average IQ of an entire Brute pack is -17. Brutes had to modify certain aspects of Covenant technology in order to account for their stupidity. For example, Phantoms were modified to have giant holes in the side that the Brutes could jump out of, since they were too stupid to work the gravity lift, and many of them were too fat to fit through it. This, along with several other changes made to Covenant technology, was seen as heresy by the Elites who worshipped Rtas Brand Heavily Armoured Toilets and Urinals.
When the Brutes were elevated to the position of Commanders of the Covenant Navy and Honour Guards to the High Prophets, the Elites declared war on them and burned their mongrel hides. Despite the Brute's superior numbers, higher quantity of ships and locational advantage, their entire army and every single Brute in existence (save for Hermitus the Hermit) was annihilated by the Elites and their Human allies at the end of the Elite-Brute War. And thus ends the pathetic tale of the Brutes.
The only Brutes to survive the slaughter were the Brutes of the Banished, a rare example of a genuinely competent Brute recruiting other compentent Brutes to form a vaguely competent organization.