Boris, also known as "Big Black Boots Boris the Bully", is a giant bully who wears big black boots.
He used to constantly kick sand in young Heinz Doofenshmirtz's face, especially in places where one would not expect sand. Apparently, he bullied Doofenshmirtz when he was playing in the sandbox, on his first date, and even when he was balancing his checkbook. In contrast, the one place Heinz was expecting Boris to kick sand at him was the beach, and even though Boris did not do so, Heinz was unable to enjoy his visit due to continuing to expect it to happen.
When Boris moves to the Tri-State Area across the street from Phineas and Ferb's house, Doofenshmirtz tries to get back at him with a giant sand kicking machine consisting of a huge brown boot and a big bucket of sand, but as usual his plan backfires on him by a wind current blowing the sand back ("The Flying Fishmonger").
Norm reveals that the bully owns a car dealership and since he couldn't come to Doofenshmirtz's backstory show, he sent him some sand. ("This Is Your Backstory")