Short answers, pulled from the story.
The name Lutheran originated as a derogatory term used by German theologian Johann Maier von Eck during the Leipzig Debate in July 1519. Eck applied it following the Catholic practice of naming a heresy after its leader. Martin Luther disliked the term and preferred "evangelical"; Lutherans themselves began adopting it in the mid-16th century to distinguish their movement from Anabaptists and the Reformed tradition.
Lutheranism teaches that humans are saved by grace alone, through faith alone, on the basis of Scripture alone. Lutherans hold that faith itself is a gift created by the Holy Spirit through the Word and Baptism, not a human decision. This means good works follow justification as its fruit but do not cause salvation.
Lutheranism spread through Scandinavia during the 16th century as monarchs adopted the faith. Christian III advanced the Reformation in Denmark-Norway in 1536. In Sweden, Lutheranism became the official religion in 1593, when the Uppsala Synod declared Holy Scripture the sole guide for faith and accepted the unaltered Augsburg Confession of 1530. Regular Lutheran services have been held in Copenhagen since 1520.
Lutherans teach that the true body and blood of Christ are present "in, with, and under" the bread and wine of the Eucharist, a doctrine called sacramental union. This differs from Catholic transubstantiation and from the Reformed view that communion is only a symbol or memorial. The Eucharist is celebrated as the central act of worship, especially on the Lord's Day.
There are approximately 90 million Lutherans worldwide, found across all continents. Lutheranism has experienced particular growth in Africa and Asia in the 21st century, as well as among young adults in the West. The Lutheran World Federation operates Lutheran World Relief in more than 50 countries.
The Book of Concord, published in 1580, contains ten documents that many Lutherans consider faithful and authoritative explanations of Holy Scripture. It includes the three historic ecumenical creeds and seven Reformation-era confessional documents, among them the Augsburg Confession and the Formula of Concord, which was signed by over 8,000 church leaders. Not all Lutheran churches treat the Book of Concord equally; Scandinavian state churches, for example, recognize only the Augsburg Confession as a summary of the faith alongside the three ecumenical creeds.