William Penn was born October 14, 1644, in London, England. He was the son of Admiral William and Margaret (Jasper) Vanderschuren Penn. His father was an English admiral, a landowner, and was knighted by King Charles II; his mother, Margaret Jasper Vanderschuren, was the daughter of a merchant.  William was the brother of Margaret, Mary and Richard Penn.
Baptism 23 Oct 1644 All Hallows Barking - notes his parents were of the Tower Liberty. 
William was a Friend (Quaker)
Although a member of a distinguished Anglican family and the son of Adm. Sir William Penn, Penn joined the Religious Society of Friends or Quakers at the age of 22. The Quakers obeyed their "inner light", which they believed to come directly from God, refused to bow or take off their hats to any man, and refused to take up arms. 
Tower of London, c.1670
Penn was a close friend of George Fox, the founder of the Quakers. These were times of turmoil, just after Cromwell's death, and the Quakers were suspect, because of their principles which differed from the state imposed religion and because of their refusal to swear an oath of loyalty to Cromwell or the King.
William Penn, as a Quaker, was persecuted for his beliefs in England. He was imprisoned in the Tower of London for seven months during 1668-69 for pamphleteering.
William Penn was a member of the Monthly Meeting of Upperside, Buckinghamshire and is mentioned several times in the "Minute Book of the Monthly Meeting of Upperside, Buckinghamshire 1669-1690" between 1671 and 1676. His first marriage, the birth of several of his children and several family burials were recorded in the Upperside registers.
Penn founded Pennsylvania as a bastion of religious freedom. It was one of two colonies, along with Rhode Island, that tolerated Quakers . Penn wanted to establish a colony where people could live harmony:
Ferris, J. L.(1680). The Birth of Pennsylvania.
Consequently, on June 24, 1680, Penn asked King Charles II (1660-1685) for a charter for land in America. The only available tract in eastern North America lay west of New Jersey, north of Maryland, and south of New York, an area that England had conquered from the Dutch in 1664 and which the King had given to his brother James, the Duke of York. After appropriate discussions the King granted Penn's request on March 4, 1681.
William married twice, and had a large family, although sources disagree about the exact number of children he had. Many of his children died young.
The Minute Book of the Monthly Meeting of Upperside includes the following entry:
Att a Meeting at Tho: Ellwood's on ye 7th of 12 th mo: 71.
Intention of marriage between William Penn of Walthamstow in the County of Essex and Gulielma Maria Springett of Tiler End Green in the parish of Penn in the County of Bucks. Thomas Zachary & Thomas Ellwood appointed to inquire.
William Penn and Gulielma Maria Springett married on the 4th of the 2nd month of 1672 (4 April 1672 new style) at King's, Charlewood, Hertfordshire. The certificate was signed by 46 witnesses. Gulielma was the daughter of Sir William Springett (1620-1644) who died before she was born and Lady Mary Springett who later married Isaac Penington. They had the following children:
Gulielma Maria (born and died 1672/3)
Margaret (1673/74 - 1674/5)
William (1673/74 - 1674)
Springett (1675/6 - 1696)
Letitia (1678 - 1746) m. William Awbrey (Aubrey)
William, Jr. (1679/80 - 1720)
Unnamed child (born and died 1682)
Gulielma Maria (1685-1689)
Two years after Gulielma's died, he married Hannah Margaret Callowhill, the 25-year-old daughter of Thomas Callowhill and Anna (Hannah) Hollister. Penn was 52. They had eight children over a twelve year period:
John Penn (1699/00–1746). Single.
Thomas Penn (1700/01–1775) m. Lady Juliana Fermor
William Penn, his second wife Hannah, and daughter Letitia Penn (by his first wife) sailed out of the Isle of Wight on September 3, 1699 on the Canterbury, or Canterbury Merchant. The ship reportedly survived an attack by pirates during the voyage, which ended December 3, 1699 at Philadelphia - a city planned and developed under Penn's direction.
Death and Legacy
Although a slave owner, Penn is remembered for peaceful tolerance. He forged a treaty with the local Leni Lenape Indians and saw that the tribe was respected and the terms of the treaty honored, saving the colony from the conflicts and attacks other English colonies suffered. 
William Penn contributed significantly to our form of government in the United States. Penn’s belief that “Religion and Policy…are two distinct things, have two different ends, and may be fully prosecuted without respect on to the other” took hold and became one of America’s most important ideals the separation of church and state which is the basis for religious freedom. 
Quakers believed that everyone had to seek God in his or her own way. Penn also thought that religious tolerance – or “liberty of conscience” – would create stronger governments and wealthier societies. Penn was unique among his fellow philosophers in that he had the opportunity to act on his beliefs. In Pennsylvania, religious tolerance was the law.  William Penn's belief that this would create wealth was disappointed. He had hoped that his colony would be profitable for him and his sons. It never became so:
William Penn died penniless on 30 July 1718, at his home in Ruscombe, near Twyford in Berkshire. He was buried on 5 August 1718 in an unmarked grave next to his first wife in the cemetery of the Jordans Quaker meeting house near Chalfont St Giles in Buckinghamshire in England. His wife as sole executor became the de facto proprietor [of Pennsylvania] until she died in 1726.
William Penn and Hannah Callowhill were declared US Honorary Citizens by Ronald Reagan in 1984.
↑ 16.016.1 "Penn owned at least 12 slaves," but "gradually came around to advocating abolition." When he died, Pennsylvania was still, "a long way from ending the practice." (Pennsylvania slavery by the numbers. www.ushistory.org).