Our Firm

Our History


From its origins as the industrial property agency of Momsen, Leonardos & Cia, our firm inherited an invaluable legacy: highly-qualified professionals offering a full range of services aimed at protecting, enforcing and making commercial use of intellectual property rights and assets held by leading companies from a myriad of industries around the world.

Over the past century, we have contributed to the growth of intellectual property in Brazil, while developing and maintaining unique expertise in that field of the law.


In 1919, American attorney Richard P. Momsen opened a law firm in Rio de Janeiro, which subsequently became Momsen & Harris. His first partner, Simeon W. Harris, descended from American immigrants who arrived in Brazil after the American Civil War. In 1927, Thomas O. Leonardos joined the firm, which became known in 1944 as Momsen, Leonardos & Cia.
By the end of the 1950s, a second generation of partners had joined the team. Through their years of service, Tomaz Francisco Leonardos and his brothers, along with Carlos Henrique Fróes and Walter Pinho, continued the standard of excellence for which the law firm had become known.

During the 1990s, the firm recruited new partners. At the same time, Filipe and Gabriel began working at the firm, marking the third generation of Leonardos family participation.

In 2012, the law firm undertook important structural changes that began another successful chapter in its history. Gabriel and Filipe Leonardos and Elisabeth Kasznar joined forces to create the intellectual property firm of Kasznar Leonardos. After partially separating from Momsen, Leonardos & Cia, the association ushered in a new era for the firm, including revamped leadership, staff and goals. With its new direction, our firm still carries in its DNA 100 years of credibility, efficiency and ethics inherited by Kasznar Leonardos, a modern and professional law firm committed to equality and diversity, as well as promoting new talent and supporting worthy social causes.


Thomas Othon Leonardos (1906-1990) founded Momsen, Leonardos & Cia, and raised his two sons, Maurício Leonardos and Tomaz Francisco Leonardos, to become Kasznar Leonardos consultants.

He was also the grandfather of attorneys Gabriel and Filipe Leonardos. Click here to read an article by renowned academic Aurélio de Lyra Tavares published in the Commercial Journal (Jornal do Commercio) in 1990.

Thomas was recognized not only as an accomplished jurist, but also as a genuinely decent man. Brazilian Lawyers’ Institute colleague Ives de Oliveira honored him with a speech on his 80th birthday. Click here to read the entire text.

Even after Thomas’ death, his grandsons and other partners continue to leave their indelible mark on the field of intellectual property.


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