**Waclaw Sierpinski was a Polish mathematician of the
XX century very known in his country but also all around the world in the
mathematics history and particularly for his works on set theory.**

**Waclaw Sierpinski was born the 14th of March 1882 in
Warsaw (Poland). This was during the Russian occupation of Poland so it
was difficult for the young gifted man to continue his studies. Indeed
the Russians wanted to keep illiteracy in Poland as high as possible so
they discouraged learning. But he succeeded entering the Department of
Mathematics and Physics of the University of Warsaw in 1899. The University
has become Russian in 1869 and all the staff was Russian. He was attracted
by the work of one of his teachers Voronov who worked on the number theory.**

**Sierpinski graduated in 1904 and began working as a
mathematics and physics teacher in a girls school in Warsaw. After the
school closed because of a strike, he went to the Jagiellonian University
in Cracow to study for his doctorate. He learnt mathematics but astronomy
and philosophy too. He received his doctorate and was appointed to the
university of Lvov in 1908.**

**Sierpinski started working on the set theory in 1907
and in 1909 he gave the first ever lecture course devoted entirely to set
theory. From 1908 to 1914 he wrote a lot of research papers and three books
on the subject : The theory of irrational numbers (1910), Outline
of set theory (1912) and The theory of numbers (1912).
He introduced the theory of the Sierpinski triangle in 1916.**

**When the First World War began, Sierpinski and his
family were in Russia and the Polish question was a political weapon between
Austria and Russia; he was interned in Viatka. Other mathematicians help
him and he was allowed to go to Moscow where he worked for the rest of
the war years with Luzin on the analytic sets. In 1916 he was the first
to give an example of an absolutely normal number (number whose digits
occur with equal frequency in whichever base it is written).**

**After the War, he went back to Lvov but shortly after
he was offered a post at the University of Warsaw that he accepted. In
1919 he was promoted to professor at Warsaw and spent the rest of his life
there. In 1920 he founded the important mathematics journal Fundamenta
Mathematica specialised in papers on set theory. Sierpinski was also
involved in the development of mathematics in Poland and was honoured to
the Polish Academy in 1921.**

**In 1939 his life changed dramatically with the Second
World War but he continued to work in the 'Underground Warsaw University'
while his official job was a clerk in the council offices. Then he managed
to send his papers in Italy. In 1944 the Nazis burned his house destroying
his library and personal letters. He lost a lot of colleagues and
students in the war.**

**He retired in 1960 as professor after having written
more than 700 papers and 50 books ! But he continued to give seminar on
the theory of numbers up to 1967 and to work as editor for several mathematics
journals. He received so many honours that it is impossible to mention
them all, for example he was awarded honorary degrees from the University
of Lvov (1929), Sofia (1939), Prague (1947) and Moscow (1967). One of the
moon craters handles his name, like many other well-known scientists.**

**He died the 21st of October 1969 in Warsaw.**

**For the anecdote, one of his students wrote of Sierpinski
that "He did not like any corrections to his papers. When someone suggested
a correction he added a line to it : 'Mr X remarked that ...' ".**