Australian-born impressionist John Russell isn't a household name — but perhaps he should be.

He was a friend of Vincent van Gogh and a mentor to Henri Matisse, so it's hard to believe that when he died at home in Sydney in 1930 he was virtually unknown in his homeland.

It wasn't until after his death that historians began piecing together his remarkable career, including 40 years working in France.

John Russell, carte de visite, c1883 ( Supplied: Art Gallery of NSW Archive )

"It has been said that Russell was an artist who was in the right place at the right time," said Wayne Tunnicliffe, head curator of Australian art at the Art Gallery of New South Wales, where the first retrospective of John Russell's art in four decades is on display.

"But it's worth remembering, in Paris in the 1880s there were thousands of artists in the right place. Very few of them had Russell's experience.

"Very few had Russell's ability to discern what was most interesting in art, meet the most interesting artists and take that into their own practice."

Van Gogh wasn't just a friend, he greatly admired the work of John Russell.

So did French sculptor Auguste Rodin.

Russell also explained contemporary colour theory to a young Matisse.

"This was transformative for Matisse's practice," Mr Tunnicliffe told 7.30

"Prior to that [Matisse] painted in a very conservative, realist style.

"Russell allowed him to free himself up, to embrace colour, to loosen up his brush work and really embrace experimentation in his practice."

Friendship with Van Gogh

John Russell inscribed his painting of Van Gogh, something he often did with portraits of his friends. ( Supplied: Van Gogh Museum Amsterdam )

Vincent van Gogh is widely seen as a tortured genius who severed his left ear and finished himself off with a gunshot.

But the celebrated Dutch painter was also an enthusiastic networker who had many friends, according to Nienke Bakker, a senior curator at Amsterdam's Van Gogh museum.

"He really had this urge to exchange with [other artists], to discuss with them about art, about colour," Ms Bakker told 7.30.

"He didn't always manage to keep his friends because he could be very difficult to get along with, but the image of the isolated artist is not at all true."

Letter from John Russell to Vincent Van Gogh, July 1888 ( Supplied: Van Gogh Museum (Vincent van Gogh Foundation) )

In the autumn of 1886 Russell painted a portrait of Van Gogh that he inscribed with the French word "amitie", meaning friendship.

The pair kept in touch, exchanging letters until Van Gogh's death in 1890.

"There's one written account about Russell's mistress Marianna being terrified when this carroty-headed artist [Van Gogh] would pop up under the studio window, sort of hissing and gesticulating," Wayne Tunnicliffe said.

'He died in obscurity' but John Russell finally recognised

Van Gogh Museum curator Nienke Bakker standing between a Van Gogh self-portrait (l) and a Van Gogh portrait by John Russell (r) ( ABC News: Alex McDonald )

John Russell returned to Australia in the early 1920s but kept a low profile.

"He painted watercolours and the occasional oil," Mr Tunnicliffe said.

"But it was private practice by this stage. He wasn't interested in showing it to other artists or exhibiting it publicly."

For Hugh Russell, it is fitting the exhibition of 120 paintings, drawings and watercolours is happening in his great-grandfather's hometown.

"He died in obscurity having spent and given away most of his significant fortune," he told 7.30