In a tweet announcing his vice presidential pick, Joe Biden described Kamala Harris as "a fearless fighter".
Mr Biden himself has felt the brunt of that fighting spirit.
During the first Democratic debate Kamala Harris, who was also seeking the party's nomination, went on the attack against the former vice president.
She criticised him over his record on race and when the two shook hands before the next debate, Joe Biden told her "Go easy on me kid".
He won't want her to "go easy" on the Trump campaign now that she's on the ticket.
Kamala Harris is a strong debater. She is tough and she'll need to be over the coming weeks.
A running mate should help the campaign and make up for any gaps or deficits the presidential candidate may have.
Joe Biden is not the strongest media performer but now he has a "fearless fighter" in his corner.
For months, Mr Biden has said he would choose a woman as a running mate.
He never said it would be an African-American woman but there was growing calls for that to happen following the recent wave of racial unrest and the resurgence of the Black Lives Matter movement.
Kamala Harris has been the favourite for some time.
She has an impressive CV as a US senator, former prosecutor and former state attorney general of California.
Some of her critics say she was too tough as a prosecutor who didn't do enough to investigate police shootings and wrongful convictions and failed to bring about reform.
Because of Joe Biden's age there is a lot of speculation that if he wins in November he will only be a one-term president and won't run again in 2024.
That means that Kamala Harris could be getting ready for the Oval Office far sooner than previous vice presidents and the "fighter" will have a fresh election battle on her hands.