A lion, a cow, a goat, and a sheep were working together as partners.
They managed to kill a stag, and the lion divided their prize into four equal parts.
"The first part is mine," he said, "because I am the lion. The second part goes to me because I am the strongest. Next, I will take the third part for myself on account of my exceedingly hard work. Finally, if anyone so much as touches the fourth part, they will know my wrath!"
That is the lion's share: he pretends to share, but he takes it all for himself.
Inspired by: Mille Fabulae et Una, a collection of Latin fables that I've edited, free to read online. I am not translating the Latin here; instead, I am just telling a 100-word version of the fable.
Notes: This is fable 16 in the book, which is Perry 339.