Maine Coon Cats are dubbed the "Gentle Giants". These cats are considered fully grown after 4 - 5 years! Reminds me of my Linus and Lucy kitties. They are Russian Siberian Forest cats. They're the second largest cat on Earth-second to the Maine Coon.
next time the animal shelter notes that the big, long-haired cat you're interested in is "part Maine Coon", chances are it's not, it's just a big, fat long-haired street cat (but adopt it anyhow! Ask yourself if it looks like THIS guy ?