Leonardo (Leo for short) is the protagonist of Little Einsteins. At 6 years old, he (as well as June) is the oldest of the group. He is the Little Einsteins' leader and the one who pilots Rocket. He is also Annie's older brother.
Leo has red spikey hair, large teal glasses, and green eyes. He wears a black short-sleeved t-shirt which has an orange streak, orange cargo shorts with large pockets, white socks, and orange and black sneakers.
His friends are June, Annie, Quincy, and Rocket. He also has other friends, but some are not human (for example, one of his friends is a bumblebee from Africa).
Also, he made meet-and-greets with people, just like the other Little Einsteins, except Rocket.
He is the only character on Little Einsteins to wear glasses.
His skills with the baton include the ability to conduct animals (seen in Our Big Huge Adventure, where he conducts cows and The Song of the Unicorn).
His main talent is conducting and his most precious object is his conductor's baton; he never leaves home without it.
Although he is only six years old, he is tall, in fact, he is taller than Quincy and his little sister Annie (she is the smallest). But June is as tall as him, but although she is tall she is small.
It is hinted that he might have a crush on June. An example was in the episode "Ring Around the Planet". After Leo got Saturn's ring back home, June walked to him and gave him a big hug. (You can see Leo smiling because of the hug).