Bilbo Baggins:

Born in the year 2890 of the Third Age, Bilbo was a bachelor, who was chosen by Gandalf to make up the lucky number for the Quest for Smaug's treasure in 2941. Needless to say, the Dwarves were not particularly amused with Gandalf's choice (thinking him more of the type of a grocer or some other tradesman) until Bilbo warned them of the crack in the wall of the goblins cave, rescued them from the spiders in Mirkwood, and freed them from the Woodelves. In the process of doing all this he found a magic ring which he used to help the Dwarves, though he kept it secret as long as he could. After he returned from his "holiday" as he often chose to call it, a year later, Bilbo settled down to write his diary, which we know under the following titles:

The Hobbit
The Hobbit, There and Back Again

In the year 3001, of the Third Age, and Bilbo's 111 birthday, he disappeared and left Bag End to Frodo Baggins, his nephew. After he disappeared, Bilbo traveled to Dale, and saw the changes the Dwarves had made, and then back to Rivendell where he stayed until after the War of the Ring when he sailed into the West with the Keepers of the Three Rings and Frodo, the other Ringbearer.

Bilbo wrote the early parts of the Lord of the Rings, which shows in the tone of the early parts of the tale. However, he gave it to Frodo to finish as he was getting too sleepy, as he said, and is recorded in the Lord of the Rings.

Bard the Bowman:

Descended from Girion, the ruler of Dale when Smaug destroyed it, Bard was an extraordinary archer. It was his arrow, the Black Arrow, that killed Smaug in the defence of Lake-Town. He also fought in the Battle of the Five Armies. Afterwards, he rebuilt Dale and became it's first ruler.

Beregond:

A Man of Gondor, and one of the Guard of the Citadel in Minas Tirith, Beregond risked his life to save Faramir, the younger son of Denethor the Steward of Gondor. Through his actions, Beregond managed to delay long enough to save Faramir's life, but in the process he broke several of the rules governing the Guard of the Citadel. He was removed from the Guard, and marched with the Host of the West. After the victory, it was Aragorn's judgment that Beregond would not be allowed to rejoin the Guard, but he became the captain of the White Company, the guard of Faramir, in Ithilien, because what he did was for love of Faramir. Beregond risked his life with this deed, as of old the punishment was death.

Bergil:

Bergil was the son of Beregond, and Pippin's guide in Minas Tirith. During the time of the War of the Ring, Bergil refused to leave Minas Tirith, and spent the time running errands for the Houses of Healing and for others.

Boromir:

Boromir, the son of the Steward Denethor, was one of the Nine Walkers of the Company of the Ring from the time it left Rivendell to the Falls of Rauros, where he was slain by orcs. Near the end, Boromir fell to the lure of the Ring, and attempted to kill Frodo. Though he repented, Frodo had already fled across the River with Sam. In the search for them, Boromir followed Merry and Pippin into an ambush of Saruman's orcs, with reinforcements from Mordor. He was slain and Merry and Pippin taken by the orcs.

Beren:

Beren was the son of Barahir. The first of the Secondborn to wed with one of the Eldar, Beren was sent on a quest to recover one of the Silmarils for King Thingol of Doriath in the First Age of the Sun. With the aid of Lúthien Tinúviel, he succeeded in the quest, and died when the Werewolf Carcharoth wounded him before being himself killed.

Lúthien however chose to die also, and so powerful was her song before Mandos, that he was moved to pity, which has never happened before or since, and granted both of them a second mortal life, after which they would die and leave the circles of the World as is the fate for Men.

Barahir:

The father of Beren, Barahir saved Finrod Felagund during the Dagor Bragollach. After the battle, Barahir led a group fighting against Morgoth. He was killed after a betrayal by one of his men named Gorlim.

Bifur:

One of the twelve dwarves who accompanied Thorin on the quest for Smaug's treasure. He survived the Battle of the Five Armies. No date is given for his death.

Bombur:

One of the twelve Dwarves that accompanied Thorin on the quest for Smaug's treasure, Bombur was notoriously fond of his food. During the quest, he fell in the enchanted river in Mirkwood. He slept for several days at least. Bombur survived the Battle of the Five Armies, and probably the War of the Ring though he was very fat and most likely did not participate in the defense. No date given for his death.

Bofur:

One of the twelve Dwarves who accompanied Thorin on the quest for Smaug's treasure, Bofur survived both the quest and possibly the War of the Ring.

Balin:

One of the twelve dwarves who accompanied Thorin on the quest for Smaug's treasure, Balin survived the Battle of the Five Armies, and later visited Bilbo in Hobbiton. Sometime between the end of the Quest of Erebor, and the beginning of the War of the Ring, Balin led an expedition to Moria to attempt to recolonize it. It was unsuccessful and all the Dwarves died.

Barliman Butterbur:

The innkeeper at Bree, Barliman Butterbur was a busy man who loved to talk, but was often known to forget important things. He was a good man, trusted by Gandalf, and by Strider (Aragorn). His inn, the Prancing Pony was well known as far away as Buckland in the Shire. After the attack of the Nazgul, Butterbur paid twelve silver pennies for the pony named Bill to replace the ponies belonging to Meriadoc Brandybuck. Later it turned out that the ponies had returned to Tom Bombadil who sent them to Butterbur. So he got five ponies for the twelve pennies.

Bungo Baggins:

The father of Bilbo Baggins, Bungo had Bag End excavated as a family residence for himself and his wife Belladona Took.

The Lord of the Rings
The Silmarillion
The Hobbit
The Complete Guide to Middle Earth by Robert Foster