Abraham, also called Abram (his birth name) was a biblical patriarch who was the ancestor of many nations, most significantly of God's chosen people - the Hebrew Israelites. He was a prophet of the true God, who made a covenant established with him, that from his descendants a great nation would emerge. The sign of this covenant was the ritual circumcision of all males within the family and tribe. The covenant would be expanded to include "many nations." He was the founder and patriarch of the line of Isaac, David, and Solomon, which makes him a direct, yet very distant, ancestor to Jesus Christ.
In his middle ages, Abram was brought out of Ur to Harran in the region settled by Aram, Shem's son. There he was called by the LORD at the age of 75. Though promised children, his wife Sarai was barren, so the couple would take matters into their own hands, giving their Egyptian slave Hagar over to Abraham to bear him a son, Ishmael.
When Ishmael had become a teenager, his aged father and "stepmother" (aged 100 and 90, respectively) would miraculous have a child named Isaac (Heb: Laughter)! The year before that, though, the "cities of the plain," including Sodom and Gomorrah, would be destroyed, even though Abraham had plead for their safety for his nephew Lot's sake.
At age 137, Abraham married his wife Sarah and arranged a marriage for his son Isaac. Soon thereafter he married his concubine Keturah, by whom he would have six sons. These sons would go on to establish tribes outside of Abraham's immediate influence. However, some of the tribes would interact with his descendants of Jacob and Moses.
Abraham would live to be 175 years old, seeing the birth of his twin grandsons, Esau and Jacob. His estranged son Ishmael would be reconciled with his brother Jacob when the two of them buried Abraham beside his wife Sarah at cave of Machpelah, near Mamre.
Abraham comes the Hebrew ????????? (transliterated: 'abrâhâm)??, which means "father of many". It comes from the Hebrew word ??? (transliterated: 'âb), meaning "father", and an unused root word that probably means "to be populous".
Abraham was born as Abram, a son of Terah and brother of Nahor and Haran. Abram was born in the city of Ur an advanced city-state civilization. It is here where Abram likely practiced a pagan Chaldean religion along with his father and Nahor. Sometime during his life in Ur, Abram's brother Haran died.
Abram married his niece Sarai. Although both Nahor and Haran had fathered children, Abram found that Sarai could not have any. At some point Abram became a Yahwist, and worshipped the true God rather than the pagan Chaldean religion of the Urites. Sometime after his son Haran died, Terah took Abram, Sarai, and Abraham's nephew, Lot to go to Canaan. While it is not known why they left Ur, some suggest it was in fact that Abraham and his whole family had become Yahwists; and that God had already called Abraham to leave. However, once they reached the city of Harran, they decided to settle there.
Calling from God
After Abram had lived for some time in Harran, God called him to leave Haran and head for Canaan, whether this was a reminder of a previous call from Ur or a new one. Leaving the city of Harran would have been significant for Abram as going into Canaan would mean going into an unknown region without any prior knowledge of the conditions. At the time the stereotypical view Canaan as completely nomadic and uncivilized.
In obedience, Abram left at the age of seventy-five years old and brought his wife, nephew, his servants and possessions and left for Canaan.
Abram then settled in Shechem, Canaan. Though the Canaanites had occupation of the land, God assured Abram that his descendants would inhabit the land. Therefore, Abraham built an altar to honor God. Abraham and his extended family set up camp, in between Bethel and Ai. Soon afterwards Abraham continued south to the Negev to further explore and occupy the land.
Refugee in Egypt
A famine came upon the land that the Hebrew family was living in, so they traveled to Egypt to become refugees during the severity. Fearing that the Egyptians would covet Sarai for her beauty and assassinate him, Abram asked her to pretend he was his sister. Sarai agreed and when the officials of the Pharaoh saw her they took her to be the wife of the Pharaoh. During the time when Abram's wife belonged to the Pharaoh he became a nobility and grew greatly in wealth, acquiring many animals and servants. While Sarai was wed to the Pharaoh, Abram may not have even had any contact with her during the time. Nevertheless, Abram would've been more than comfortable living in Egypt as a refugee during the famine. Abram not only gained wealth and lived comfortably, he also received special attention from the Pharaoh.
Seemingly the famine ended while Abram was in Egypt, however, he did not return to Egypt but remained as a refugee there. As a consequence of the false marriage (and perhaps abandoning Canaan) God inflicted diseases on the Egyptian Monarch's household, brought to them by the foreign wife of the Monarch. Abram was summoned before the King who had realized he had been deceived and so he sent Abram and his wife away. The Father of the Hebrews left Egypt along with his wife, nephew and all of his wealth.
Return to CanaanDivision with Lot
After leaving Egypt, Abram went to living nomadically for some time. He eventually returned to his original choice of settlement in between the cities of Bethel and Ai. Abram and his nephew Lot both lived in this area. Now after they had left Egypt, Lot gathered cattle and had many herders under him. Due to the lack of adequate resources to care for both of their herds, the herders began fighting over land ownership. To solve the conflict, and to avoid angering the native locals, Abram asked Lot to choose a direction to move where he would move opposite. Upon surveying the land Lot chose to live among the cities of the plain of Sodom and Zoar, whereas Abram lived out in the wilderness.Settling near Hebron
After Lot and Abram took their separate areas, the LORD spoke to Abram and promised that all the land surrounding him would belong to his descendants, permanently. Abram was told that his descendants would be numerous as dust and then was told to spread out and explore the land of his descendants.After exploring the land that the Hebrews would one day fill, Abram settled in the Mamre Forest, near the city of Hebron.
Battle with Kedorlaomer
During Abram's time in Hebron a war began between the kings of the nearby city-states. This war lead to an alliance of city-states allied under the Elamite King Kedorlaomer against the city state of Sodom and its allies. As a result Sodom was raided by Kedorlaomer's force and Abram's nephew, Lot was captured along with his possessions.
A man who survives the battle goes to Abram and warns him. This is the first usage of the word "Hebrew" in the Bible, as the Book of Genesis's author Moses uses it as an epithet for Abram: Abram the Hebrew. When the Hebrew heard the news of his nephew's capture he gathered three-hundred and eighteen battle trained men under his service, along with support from his allies and pursued the army. After dividing the men and engaging in battle Abram recovered all the possessions of all the Sodomites. He restored his brother Lot to the city along with all the people who had been captured in the process.
So the King of Sodom came out to meet with Abram along with the High Priest King Melchizedek of Salem (Jerusalem at the time). Melchizedek gave praise to Abram and God, so Abram gave him a tenth of all the goods retrieved. Sodom's King even offered Abram the rest of the items he had returned, except for the people of Sodom. Abram refused stating he had made an oath by God that he would not accept anything belonging to the King of Sodom; except for each man's food and spoils.
Child CovenantGod's Promise
At this time Abram had no son, due to the infertility of his wife. Thus, he made his highest servant Eliezer of Damascus the heir to his estate. When the word of God came to Abram telling him not to be afraid, Abram asked God what he could give him if he had no son of his own. Yahweh replied by telling him that the heir of estate would not be his servant Eliezer, but a son of his own. So the rich Hebrew believed God's promise and it was considered righteous.
Abram also asked for a sign to know whether or not for sure his far offspring would occupy the land of Canaan. Doing what was instructed by the LORD, Abram brought several animals and sacrificed them on an altar. That night as he was sleeping a fiery pot passed between the altar and God made a covenant that the descendants would inhabit the land from the Wadi of Egypt to the Euphrates River.Sarai Intervenes
After this, Abram's wife, Sarai concerned of her infertility asked her husband to sleep with her Egyptian slave Hagar. Doing this was the only way to fulfill God's covenant of Abram having an heir of his own blood, so she thought. Abram agreed to do this and so he slept with Hagar, conceiving a son. When Hagar learned of her pregnancy she became towards her master Sarai, who then blamed Abram for her newfound attitude. Abram told his wife to do whatever she pleased with Hagar, and so she mistreated her.
As a result, Hagar ran away but she returned to have her son after the LORD asked her to return. At the age of eighty-six Abram had his first ever son, with a concubine who was not his wife. He named him Ishmael as this was the name that was given to Hagar by God for the child. 
The Covenant with AbrahamRenaming and Promise of many nations
Thirteen years, at the age of ninety-nine later God appeared to Abram and officially made a covenant with Abram. Prior to this He had made many promises and assurances, but this covenant made it a legally binding agreement. When Abram heard God about to make his covenant he fell facedown and prostrated before the LORD. He then told Abram that he would be the father of many nations, thus he would no longer be called Abram, but Abraham. The name Abraham means "father of many nations", which shows this renaming was an epithet to mark the covenant and his occupation as such.The Mark of Circumcision
As a legally binding agreement God instituted that all male descendants and members of Abraham's household had to be circumcised. This served as a physical mark and indication of the covenant between Abraham and God. All the males who were not circumcised would have to be cut off from their people as outcasts. 
Not only did God make a covenant with Abraham and require circumcision, He also decreed that his wife's name would be changed to Sarah rather than Sarai; for should we be blessed as the mother of many nations. In disbelief Abraham fell facedown and laughed pondering to himself that a son could be born to a man of nearly a hundred and a woman in her nineties.
Abraham proceeded in obedience to God's decree of circumcision and every male in his household was circumcised, meaning Abraham was circumcised at the age of ninety-nine.
The Three Figures
One day, God appeared to Abraham who was sitting in the entrance of his tent, near Mamre during the hottest part of the day. Abraham spotted the LORD appearing as three figures. So Abraham went up and knelled before the figures and offered them food. God obliged and Abraham ordered his wife and servants to retrieve food to feed the visitors. As Abraham ate with the figures he was told that around the same time the next year God would return and Sarah would bear a son. Sarah who sat behind them in the tent heard this and laughed to herself.Pleas for Sodom
When God asked Abraham why Sarah had laughed, Sarah lied and said she did not. God knew this however and told her that she had laughed. As the LORD in three figures prepared to leave they looked down towards Sodom. Then God explained that the sin of the city had been great and that He planned to have it destroyed.
Conversation with a rich man
During Jesus' ministry he gave an account concerning Abraham, likely an actual account (or could have been a parable). There was a rich man who lived in luxury who neglected a homeless beggar named Lazarus.
Eventually the beggar Lazarus died and he came and was at the side of Abraham. Sometime later the rich man died. While in Hell the rich man could see Abraham so he called out to him referring to him as father. Abraham was far away in Heaven when he heard the rich man asking him to send Lazarus to provide him comfort in his torture. Rather Abraham told the rich man that in his lifetime he received good things, while Lazarus experienced bad things. Abraham went on to say that even if he were to send Lazarus, there was a great space between Heaven and Hell that could not be crossed.
Abraham continued to receive pleas, asking him to send Lazarus to his family to warn them. Still Abraham told the rich man that they had the Old Testament Law and Prophets to look at for guidance in living. The rich man continued asking "Father Abraham" to send Lazarus to warn his family, so that they may repent. Again Abraham said if his family did not obey Scripture, they would not repent even if they saw a spirit . If this was an actual account, this would indicate Abraham may have some dominion over his ancestors in Heaven (and maybe even Hell).
If the account was a parable or allegory, it shows the reverence by the Jews and Hebrews of Abraham as their ancestor, as he was called "Father Abraham". In addition he was an important "spiritual figure" which shows his importance to the culture, being parabolic in this case.