Armstrong never knew his real birthday: he always claimed 4 July 1900. The little boy with the gaping mouth (the 'Satch', short for 'Satchelmouth', was bestowed on him from an early age) lived in the characteristically abject conditions of many New Orleans blacks, working at menial jobs to earn a dollar and living largely as a street urchin. He bought a cornet from a pawnshop but was detained after setting off a pistol on New Year's Eve, 1912, and sent to a waifs' home, where the bandmaster gave him lessons and soon had him leading the band. On his release, he delivered coal and played in local bands before coming under the wing of Joe Oliver, whom he idolized. Soon enough he was playing second cornet to Oliver's lead in Chicago, having previously worked in Kid Ory's band and on riverboats with Fate Marable. Their two-cornet breaks were a sensation, and if only a modest part of the band's power comes through on their 1923 records, it's still impressive enough. Armstrong married their pianist, Lil Hardin, and left Oliver to join Fletcher Henderson in New York, where his hick manners caused amusement, although his playing electrified Henderson's then somewhat stately orchestra. I Miss My Swiss (1925), which turns from a quaint dance performance to a blazing jazz record when Armstrong takes a solo, is characteristic: for the first time, we can hear jazz in terms of swing, the indefinable rhythmic propulsion which, when heard, seems to ripple through the human frame.

But he grew dissatisfied with Henderson's group and returned to Chicago in November 1925, where over the course of three years he set down the sessions for local label OKeh listed as Louis Armstrong & His Hot Five/Seven. Although the band was basically a studio group – initially Armstrong with Hardin, Johnny Dodds, Kid Ory and Johnny St Cyr – the players knew each other well. But Armstrong entirely dominates what would otherwise have been a merely interesting small group. Clear of distractions, he sets down on record after record chorus-length solos which became a clarion call to jazz soloists everywhere, unleashing all the possibilities of improvisation in the idiom. Played in an extravagantly rich, open tone, their virtuosity is stunning, their range unprecedented: Armstrong switched from cornet to trumpet around this time, and it appeared to encourage his venturing still further. Rhythmically and harmonically, he seems to be a light year ahead of every other player, and daring as the trumpet playing is, it has a poise and high finish to go with the risk-taking. Even the experienced Dodds and Ory seem overwhelmed, although Dodds sounds much better on the Seven sides. Besides the trumpet, Armstrong also began singing: the scat chorus he takes on Heebie Jeebies (1925), perhaps the first of its kind on record, is musically almost as smart as his trumpet work, and everywhere he swings the lines and makes his gravelly timbre into something bewitchingly new. By the time of the 1927–8 sides, he is Olympian: Potato Head Blues, Wild Man Blues, West End Blues and Tight Like This offer music which is still undimmed in its splendour and excitement. For the later sessions, Earl Hines came in as pianist, and their shared brilliance is well caught on Weather Bird (1928).

Away from the studios, Armstrong was being featured as a star soloist with various bands, including those of Erskine Tate, Carroll Dickerson and Clarence Jones, and eventually this became a touring position, working with Dickerson or Luis Russell-led aggregations in many cities. His records began to feature similar orchestral backdrops, and in 1933 he signed with Victor, where he made records which often amounted to mini-concertos, a vocal chorus of a popular song followed by a majestic trumpet improvisation. The best of them, such as I've Gotta Right To Sing The Blues (1933), still assert his magnificence. He travelled to Europe in 1933–4, where he received a king's welcome in many cities, his records having already gone round the world. Back home, he engaged Joe Glaser as his manager, a position which the latter held for the rest of Armstrong's life: manipulative and devious Glaser may often have been, but he made sure Louis was always looked after and protected. Armstrong moved to Decca from RCA, and while the records became more formulaic, given the right circumstances Armstrong still made delightful music. He made films and became more of a showbiz personality under Glaser's stewardship. As the big-band era declined and costs mounted, the orchestra was taken off the road and – following some very successful Town Hall (New York) concerts in May 1947 – a new group (Louis Armstrong And His All Stars) became the trumpeter's performing vehicle, initially a sextet with Barney Bigard, Jack Teagarden and eventually Earl Hines at the piano. Their earlier music was by far the best: both Hines and Teagarden soon became bored or disgruntled, and the eventual reliance on Dixieland staples as their core repertoire blunted any sense of adventure which might have remained in Armstrong's work.

Yet he seemed oblivious to shortcomings, always loving to entertain crowds, and the bravado of his early work was steadily displaced by an economy of delivery which assumed a monolithic majesty. Although his voice grew ever more scarred, his delivery was unimpaired, and as a recording artist his progress through the early LP era is fascinating: his Decca albums are an engaging mix of pop and jazz material, and the sets he made for George Avakian at Columbia include some beautiful reshapings of his jazz past, including Plays W C Handy (1954). He also partnered Oscar Peterson and Ella Fitzgerald at Verve, and in 1961 made exquisite and long-undervalued records with Duke Ellington. By the 60s, 'Ambassador Satch' had visited many countries and was all but an unofficial representative of the State Department: some regarded his mugging in these situations as offensive, but Billie Holiday summed up the feeling of many when she said that 'Sure Pops Toms, but he Toms with class'. Armstrong had never bothered too much about hurtful opinion, even when boppers derided him as a bygone, but he didn't sleep on his principles either: this generous man, who always had a roll of dollars for friends down on their luck, angrily admonished his government during the Little Rock integration crisis of 1957 and cancelled one of his tours in protest. Later in the 60s, he became a pop star once again: Hello Dolly (1964) bested The Beatles in the charts, and What A Wonderful World (1967) became such an enduring success that many who knew nothing of his jazz work thought Armstrong was an elderly pop singer. By this time the All Stars had become a tiring routine and at the end Armstrong had little left to give: his final records feature only vocals.

Although a beloved showbiz figure, he lived quietly in a Queens suburb, in a house which has now been opened as an Armstrong museum, often tapping away at his typewriter and chatting with friends. Since his death in 1971, his star has been in the ascendant again: his records are readily available, from the Hot Fives onwards, and contemporary jazz celebrities such as Wynton Marsalis have insisted on the primacy not only of the universally acknowledged early work but the rest of Armstrong's oeuvre as a potent and powerful legacy. If the world's music still swings today, it is in large part because of what he was first doing, eight decades ago.

Biography from Richard Cook's Jazz Encyclopedia (2005).

If you'd like more information, check out The New Grove Dictionary of Jazz (2002) or The Biographical Encyclopedia of Jazz (2007), both of which are still in print.