Leo Orissa was the head of a Russian Organization and was a former friend of Arvin Sloane.
Before Season 4
Orissa was born in 1947 in Moscow. He was 6' and weighed approximately 150 pounds.
He was first seen on a yacht owned by Boris Tambor and intended to buy a weapon from him called Black Thorine. However, Leo made a joke saying he'd use the bomb to take over Tambor's organization. Tambor laughed at first, but suddenly realized he was in danger when his girlfriend tried to shoot him. Leo's guards took out Tambor's guards and then Leo and Bridget cornered Tambor himself and killed him.
When Sydney was sent on the yacht to buy the bomb back from Leo, she warned him to comply otherwise Arvin would brutally torture him until he agreed. Leo finally accepted Sydney's bluff and was about to agree, but Bridget got upset over his betrayal and shot him in the forehead.