Apollonius (c262-190 BC): Alexandrian geometer author of various books including the lost book on plane loci which is known from various commentators to have given the theorem about circles associated with the angle bisectors of a triangle.
? Bodenmiller (19th century re-discovered the theorem about the midpoints of diagonals of a quadrilateral now also ascribed to Gauss.
Henri Brocard (1845-1922): discovered a number of properties associated with the points, triangles and circles now named after him.
Giovanni Ceva (?1647-?1736): discovered theorems about points on the sides of a triangle (see glossary); the one for collinear points is now ascribed to the first century Alexandrian geometer, Menelaus.
Leopold Crelle (1780-1855): engineer and editor of famous mathematical journal; he discovered various properties of triangles including the points now named after Brocard. He claimed that "it is wonderful that so simple a figure as the triangle is so inexhaustible".
Euclid (c300 BC): author of the Elements the influential systematic account of geometry including many theorems about triangles.
Leonhard Euler (1707-1783): prolific Swiss mathematician who established that certain special points of a triangle lay on a line - now named after him.
Pierre Fermat (c 608-1665): famous amateur mathematician who corresponded with many of his contemporaries; he proposed the problem of minimising the sum of the distances from a point to the sides of a triangle - the solution is now known as a Fermat point.
Karl Feuerbach (1800-1834): German schoolteacher who investigated the properties of the medial circle through the midpoints of the sides of a triangle; the theorem that this circle touches the inscribed and circumscribed circles is often named after him.
Carl Gauss (1777-1855): among his many discoveries is the intriguing property of the midpoints of the diagonals of a quadrilateral.
Joseph-Diez Gergonne (1771-1859): geometer who studied the point of concurrence of lines joining the vertices of a triangle to the points of contact of the inscribed circle.
H C Gossard (20th century): discovered theorem about the Euler lines of the four triangles formed from the sides of a triangle and its Euler line.
Ludwig Hesse (1811-1874): investigated the so-called isodynamic points which are now sometimes named after him. Emile Lemoine(1840-1912): described some properties of the isogonal conjugate of the centroid, now sometimes named after him, but more generally referred to as the symmedian point.
Emile Lemoine (1840-1912): described some properties of the isogonal conjugate of the centroid, now sometimes named after him, but more generally referred to as the symmedian point.
Christian von Nagel (1803-82): constructed a point in the same way as the Gergonne point but using the point of contact of an escribed circle; the point is now sometimes named after him.
Joseph Neuberg (1840-1926): investigated various circles associated with a triangle and a remarkable cubic curve, named after him, passing through many special points of a triangle.
Jean-Louis Nicolet (1901-1966): Swiss schoolteacher who made pioneering films - short, silent animations of some traditional geometrical themes; these were developed in computer animated versions by Caleb Gattegno in the eighties. See R. Beeney et al, Geometrical images, ATM, 1982.
Robert Simson (1687-1768): his edition of Euclid influenced most subsequent English editions; the pedal line of a triangle is erroneously named after him, due it seems to a careless ascription by a French mathematician.
? Spieker (19th century): described properties of the in-circle of the midpoints triangle.
Jacob Steiner (1746-1827): Swiss mathematician who contributed to various branches of pure geometry; a point associated with the triangle is named after him, and so is the envelope of the pedal line of a point as it moves round the circumcircle.
Gaston Tarry (?-1913): investigated a point associated with the Steiner point.
Robert Tucker (1832-1905): investigated various circles, named after him, associated with the triangle; he proposed calling the isogonal conjugates of the medians the symmedians, and their point of concurrence the symmedian point (this is also sometimes called the Lemoine point).
? Edmund Van Aubel (1900-?): discovered various triangle theorems, as well as one about the squares drawn on the sides of a quadrilateral.
William Wallace (1768-1843): said to be the first to have discovered the properties of the pedal line - now sometimes named after him though it is still often called the Simson line.