Alexander Leonidovich Mamut (Russian: Алекса́ндр Леони́дович Маму́т; born 29 January 1960) is a Russian-Israeli billionaire, oligarch, lawyer, banker and investor. Until 2020, he was a co-owner of Rambler Group.

In June 2022, Forbes estimated Mamut's net worth at $2 billion.

Alexander Mamut was born on 29 January 1960. His father is Leonid Solomonovich Mamut, a lawyer and one of the authors of the Russian Constitution. His mother, Cicilia Ludwigovna, is a defense attorney. In 1977, Mamut graduated from Moscow gymnasium #17. He studied law at Moscow State University, graduating in 1982.

Mamut began his career as a legal advisor at a printing house.

In 1990, together with Andrey Gloriozonov, Mamut founded "Business and Cooperation” Bank, that was renamed in 1991 into Commercial Bank "Imperial" with Segey Rodionov as chairman and President of the Board. The bank was founded to service companies in the field of fuel and energy. Its biggest clients were the Rem Viakhirev associated Gazprom and the Vagit Alekperov associated Lukoil.

In 1990 Mamut founded ALM-Consulting law firm (ALM abbreviated after Mamut's name) and served as Managing Partner there throughout 1990–1993. In 1991, ALM Consulting partnered with Frere Cholmeley Bischoff, a law firm based in London and headed by Tim Razzall from 1990 to 1994, in order to establish many offshore shell companies with which ALM Consulting would create the offshore shell company through Frere Cholmeley Bischoff for $300 and then ALM Consulting would sell that same offshore shell company for $5000. In 1993, Roman Kolodkin introduced Mamut to Igor Shuvalov who worked at the Russia's Ministry of Foreign Affairs in the legal department as an attache. According to an interview published in the Russian independent newspaper Meduza, Mamut hired Shuvalov as a senior advisor to ALM. On behalf of the company, Shuvalov conducted special assignments with offshore companies and transported money. Such Russian oligarchs as Alisher Usmanov, Roman Abramovich, and Boris Berezovsky were among the largest clients of ALM Consulting in the 1990s.

During the 1990s, Mikhail Kasyanov, while he was the head of the department of external loans and foreign debt at the Russian Ministry of Finance, made decisions in support of Mamut.

Mamut founded the Design Bureau "Company of Project Financing" (KOPF) (Russian: ЗАО КБ "Компания по проектному финансированию" (ЗАО КБ "КОПФ")), which is a bank, in 1993, and served as its chief executive officer until 1998. In 1996, KOPF donated 280 million rubles to Boris Yeltsin's election campaign. Meanwhile, he was the co-founder and director of Sedmoy Continent from 1993 to 1997.^{[citation needed]} He was the founder of ALM Development and remained an investor until 2001.^{[citation needed]}