Anders Johan Lexell (December 24, 1740 – December 11, 1784 (Julian calendar: November 30)) is a Swedish-born Russian astronomer, mathematician, and physicist who spends most of his life in Russia, where he is known as Andrei Ivanovich Leksel.

Lexell makes important discoveries in polygonometry and celestial mechanics; the latter lead to a comet named in his honor.

La Grande Encyclopédie states that he was the prominent mathematician of his time who contributed to the spherical trigonometry with new and interesting solutions, which he took as a basis for his research of comet and planet motion.

His name was given to one of the theorems about spherical triangles.

Lexell is one of the most prolific members of the Russian Academy of Sciences at this time, having published 66 papers in 16 years of his work there.

A statement attributed to Leonhard Euler expresses high approval of Lexell's works: "Besides Lexell, such a paper could only be written by D'Alambert or me".

(”Precis de la vie de M. Lexell".

Nova Acta Academia Scientarum Imperialis Petropolitanae 2: 16–18.

1784.)

Daniel Bernoulli also praises his work, writing in a letter to Johann Euler "I like Lexell's works, they are profound and interesting, and the value of them is increased even more because of his modesty, which adorns great men".

(Uchenaya Korrespondentsiya 62 (48).

24.02.1776.)

Lexell does not have a family and keeps up a close friendship with Leonhard Euler and his family.

He witnesses Euler's death at his house and succeeds him to the chair of the mathematics department at the Russian Academy of Sciences, but dies the following year.

The asteroid 2004 Lexell is named in his honor, as is the lunar crater Lexell.