The present article deals with two portraits of the brilliant astronomer, the citizen of Gdańsk (Germ. Danzig), Johannes Hevelius (1610–1687). One of the paintings, since 1681 has been held in the Gdańsk City Council Library, now known as the Polish Academy of Sciences Gdańsk Library. The second portrait, donated by the astronomer in gratitude for accepting him into the Royal Society of London for the Promotion of Natural Knowledge, since 1679 had been held in the Bodleian Library in Oxford, after which, in 2001, it was moved to the city’s Museum of the History of Science. Recently the barely visible, yet legible signature of Andreas Stech (1635–1697), located to the right of the astronomer’s finger touching the celestial globe: Andr. Stech | pinxit 167[?] has been discovered and deciphered in the Oxford portrait. Placed next to each other during an exhibition in Gdańsk in 2011, the paintings did not make an impression of having been painted by two different hands. The signature on the Oxford portrait settles the matter – both paintings are by Stech. The painter was constant collaborator with Hevelius, the author of the astronomer’s other portraits, including those in the frontispieces as well as scientific illustrations in the scholar’s works. The iconographic uniqueness of the Gdańsk original and the Oxford replica confirm that it was the astronomer himself who determined the painting’s iconography. Hevelius wanted to be remembered as a rational scholar with a Cartesian countenance, admiring the work of Creation but also researching it empirically. Together with the artist he rejected the vain and melancholic tradition of representing astronomers. A new type of portrait of the early modern scholar was created in collaboration between the scholar and the artist – that of the specialist in a specific branch of knowledge.