First Steps introduces the world to Mister Fantastic, Invisible Woman, Human Torch and The Thing, but there's one other character of importance.

In a 1982 arc by John Byrne, Franklin gets frustrated trying to solve a Rubik’s Cube and uses his powers to age himself into an adult body, though he couldn’t actually gain more emotional maturity. He winds up going back to being a kid, placing restrictions on his own abilities to allow him to have something of a normal childhood.

First Steps introduces plenty of characters to the MCU, but its strongest one isn't Galactus or Franklin Richards.