The development of today's English actually goes back 1500 years to the languages used by the war-like Germanic tribes of northern Europe. The four stages of this language's evolution are: Old English or Anglo-Saxon (500-1050), Middle English (1050-1550), Early Modern English (1550-1700), and Late Modern English (1700-onwards).
English, as we know it today, began primarily as a combination of those dialects brought to the British Isles by Angle, Saxon, and Jutish invaders; however, the language was also influenced by the native Celtic languages; Danish during the 9th-11th Centuries; Norman French, after the Conquest of 1066; and Latin, which was introduced by the Roman Catholic Church.
The standardization of English began in earnest with the 1525 publication of William Tyndale's translation of the New Testament, and soon after in the 1611 Authorized Version of the Bible. By the end of the 16th century, Standard English had been established. This versatile language was formally documented and recognized with the publication of Samuel Johnson's dictionary in 1755.
Today, English is the first language of about 300 million people and is used by up to 800 million users. Although Mandarin is spoken by more native speakers, English is considered a global language - many scholars call the latest stage of English World English since it is so widespread. It is also the official language of aircraft and shipping, the leading language of science, technology, computers, commerce, etc.