Nahshon ben Aminadav was the first Israelite to leap into the Red Sea. His self-sacrifice effected the splitting of the sea, and he was rewarded by having King David as one of his descendants.

When the tribes stood at the sea, this one said: I will not descend first into the sea, and that one said: I will not descend first into the sea…. While they were standing and deliberating about what to do, Nahshon leapt and descended into the sea…. Immediately, the Omnipresent said to Moses: My beloved is drowning in the sea, the sea is blocked, and the enemy is in pursuit, and you are merely standing and persisting in prayer. Moses said before Him: Master of the Universe, what am I to do? God said to him: “And you, raise your staff and extend your hand over the sea and split it” (Exodus 14:16)…. The Omnipresent said: As a reward for Nahshon, who initially treated Me as a king by obeying My will at the sea, I will make his descendant, David, king over Israel. (Mekhilta deRabbi Yishmael, Beshalah, Mesekhta deVayhi 5)