Euclid (300 BCE), sometimes called Euclid of Alexandria to distinguish him from Euclides of Megara, was a Greek mathematician, often referred to as the "father of geometry".

That, if a straight line falling on two straight lines makes the interior angles on the same side less than two right angles, the two straight lines, if produced indefinitely, meet on that side on which the angles are less than two right angles. Euclid

That, if a straight line falling on two straight lines makes the interior angles on the same side less than two right angles, the two straight lines, if produced indefinitely, meet on that side on which the angles are less than two right angles.

Give him threepence, since he must make a gain out of what he learns. Euclid

Give him threepence, since he must make a gain out of what he learns.

QED - Quod erat demonstrandum. Euclid

QED - Quod erat demonstrandum.

Better balance, less pain and less restless leg syndrome. Euclid

Better balance, less pain and less restless leg syndrome.

A line is length without breadth. Euclid

A line is length without breadth.

The laws of nature are but the mathematical thoughts of God. Euclid

The laws of nature are but the mathematical thoughts of God.

And the whole is greater than the part. Euclid

And the whole is greater than the part.

In right-angled triangles the square on the side subtending the right angle is equal to the squares on the sides containing the right angle. Euclid

In right-angled triangles the square on the side subtending the right angle is equal to the squares on the sides containing the right angle.

Sire, there is no royal road to geometry. Euclid

Sire, there is no royal road to geometry.

A prime number is one (which is) measured by a unit alone. Euclid

A prime number is one (which is) measured by a unit alone.

Things which are equal to the same thing are also equal to one another. Euclid

Things which are equal to the same thing are also equal to one another.