The donation, totaling some £2 million, is being made through the family's charitable foundation, The Exilarch's Foundation, which has in the past given financial support, guidance or has outright initiated several causes in both the UK and Israel.
“I believe that the work of RUSI has become increasingly important in these challenging times and it deserves our support,” Exilarch's Foundation Exilarch David Dangoor said in a statement.
“Our gift should help RUSI fulfil its charitable mission by providing independent, politically-unbiased analysis and information to the wider public, in the UK and overseas.”
Dangoor is a well-known Jewish businessman and philanthropist, emigrating from Iraq to the UK in the 1960s.
"I am bowled over by the generosity of the Dangoor Family and the Exilarch's Foundation," said RUSI chair Sir David Lidington.
"Given the impact of the pandemic, I was concerned that the fundraising campaign would take a hit. But this donation from David Dangoor and his family is extraordinarily welcome and a huge vote of confidence in RUSI and in our plans for the future."
RUSI Director-General Dr. Karin von Hippel added: "I regard this exceptional and historic gift as an accolade to the quality of our research, analysis and expertise, and of course, to our hardworking and talented staff. The Dangoor gift will allow RUSI to invest in its research and conference facilities, as well as our historic library."
RUSI promotes study into security, defense and military doctrine, but has in recent years expanded into financial and organized crime; terrorism and ideologies that foster terrorism; and natural disasters.