Twenty years ago I celebrated Louis Armstrong’s influence with some of my favourite musicians for The Herald Magazine, in advance of a centenary concert at that year’s Edinburgh Jazz & Blues Festival. It all still holds true – on the occasion of the 120th anniversary of the great man’s birth.

Jazz anniversaries come and go, but there is none as significant or as worthy of celebration as that of Louis Armstrong. He was jazz. No other jazz musician has had the impact or the profile that Armstrong had. While the general public remembers him primarily as a much-loved entertainer who came from a jazz background, the jazz world regards him as the single most important figure in 20th Century American music. Armstrong invented jazz as an art form, and he revolutionised popular singing. His influence was universal and enduring.

Genius springs from unlikely sources – and Louis Armstrong was no exception. He was born on August 4, 1901, in the seedy Storyville section of New Orleans. Just 21 years later, the waif who learned to play trumpet while in a home for wayward boys had musicians queuing up to hear him, and all of Chicago buzzing with talk of his brilliant on the bandstand with his mentor King Oliver’s Creole Jazz Band. His impact on jazz was immediate. His dynamic, driving playing revitalised the Fletcher Henderson band in New York in the mid-1920s. What he played one night would be copied all over town the next day. And when he first got into a studio with his own bands, specially created for recording sessions, the results turned the jazz community upside down.

The 64 sides Armstrong recorded between 1925 and 1929 with his Hot Five, Hot Seven and Savoy Ballroom Five line-ups shaped the course of jazz and are now regarded as the single most important body of work in jazz history. These were the records on which his genius burst out in all its glory for the first time. His fantastic playing – dazzling lyricism and originality, innate swing and daring stop-time solos – threw down the gauntlet to musicians everywhere. The late guitarist Danny Barker once said: “The Okeh record company released a record by Louis about every six weeks, and everybody waited for the records because each one of them was a lesson in something new; in things to come.”

Armstrong had already inspired other musicians who came to hear him, but the Hot Five records had an even greater impact. They are the DNA of jazz.

Trumpeter Max Kaminsky wrote: “Above the electrifying tone, the magnificence of his ideas and the rightness of his harmonic sense, his superb technique, his power and ease, his hotness and intensity, his complete mastery of the horn – above all this he had swing. No-one knew what swing was until Louis came along. It’s more than just the beat, it’s conceiving the phrases in the very feeling of the beat, moulding and building them so that they’re an integral, indivisible part of the tempo. The others had the idea of it, but Louis could do it; he was the heir of all that had gone before and the father of all that was to come.”

Had Armstrong never made a record after 1929, he would still be the most important figure in jazz. Critic Gary Giddens has said: “In those [Hot Five] recordings, Armstrong proves for the first time that an improvisation cane be just as coherent, imaginative, emotionally satisfying, and durable as a writer piece of music.”

As he played, Armstrong wrote the language of jazz, transforming an ensemble music into a soloist’s art. One of his contemporaries, trumpeter Mutt Carey, later remembered: “He tried to make a picture out of every number he was playing to show just what it meant. He had ideas, enough technique to bring out what he wanted to say. He made you feel the number and that’s what counts.”

Miles Davis, the trumpeter who himself broke plenty of new ground, said: “You can’t play anything on a horn that Louis hasn’t played – I mean, even modern.”

Not only did Armstrong influence his contemporaries; he has continued to influence generations of jazz musicians. Cornettist Warren Vaché says: “He was the 20th Century Beethoven as far as I’m concerned. Nobody every swung before Louis. He taught us all how to play in 4/4 time and swing like mad. He also invented the language of the trumpet and pretty much the language of improvisation, too. It just doesn’t get any better than him.”

Marty Grosz, the guitarist and singer, echoes the sentiment. “Let’s put it this way, Louis Armstrong was to jazz, or is still to jazz, what Shakespeare was to English literature. He somehow, innately, just knew what to do and when to do it. He was the bell-wether of everything that followed. He pointed the way. That’s not to say that there weren’t many other talented people, but somehow Louis rhythmically freed up the whole thing.”

Tenor saxophonist Scott Hamilton says: “There is no other single person who has had the kind of impact on how we play the music than Louis Armstrong had, and his Hot Five recordings were pioneer examples. He continued the rest of his life to influence people, and he continued to make influential recordings, but those ones from the 1920s were the ones which first showed the way.”

It’s also important to note that Armstrong showed the way, not only to trumpeters, but to players of every instrument – a rare legacy, as clarinettist and saxophonist Ken Peplowski points out. “There are a few people who have come through the jazz pantheon who do that: Charlie Parker’s one, but Armstrong was certainly the first.”

Armstrong’s phenomenal achievements as a pioneer don’t end with his trumpet playing. He was also, as Gary Giddens said in Ken Burns’ series Jazz, “the single most important singer that American music has produced.” His first big hit, Heebie Jeebies, introduced the world to his gravelly style of scat singing, and his way of improvising with his voice as freely as if it were an instrument was enormously influential.

Danny Barker said: “That’s when the song stylist came in. People began to buy records because they liked a certain personality – Louis Armstrong was responsible for that.” Billie Holiday, Ella Fitzgerald and Frank Sinatra are among those who were inspired by his looser style of singing, his way of personalising songs.

Ken Peplowski is one of a huge number of musicians – including clarinettist Artie Shaw and tenor saxophonist Coleman Hawkins – who have credited Armstrong with inspiring him to create his own music. Shaw said that Armstrong taught him “that you should do something that was your own,” something that expresses who you are. Peplowski says: “He was a great entertainer and a great artist. He didn’t compromise either of these aspects – and almost refused to. He was one of the first people who presented himself in a very natural state – take it or leave it; this is what I do.”

But the last word goes to the late trumpeter Dizzy Gillespie who memorably summed up the feelings of thousands of jazz musicians the world over when he said of Louis Armstrong: “Without him – no me.”