With these four requirements so that it isn't too easy:
1: Has to be in a 2024 state where Biden is actually on primary ballot (so no Hew Hampshire voter in the possible scenario that Biden doesn't file for that primary)
2: Has to be a voter who is actually familiar with RFK Jr, and is not just voting for the Kennedy name
3: Has to be a voter whose political views stayed relatively consistent.
4: Voted for Biden and Clinton in the general elections.
I'll give this a try. This is a voter who is generally moderate Democrat and thought Bernie was too extreme, which explains the Clinton and Biden votes. While he became anti-covid lockdowns in 2020 and disapproved of Biden's views on the issue, he strongly preferred him to Trump on other issues and still voted for him. However, this voter later became disgusted by all the money the USA spent to fund Ukraine and turned on Biden over that issue. Biden had also pissed him off with the covid19 vaccine mandate in 2021. Therefore, even though he supported Biden in the 2020 primary, he is happily supporting RFK this time around, as he agrees with RFK's anti-vax/covid lockdown policies, his anti-Ukraine funding views, combined with RFK's broadly liberal views on other issues. As for the likely Biden vs. Trump general, he was initially split between voting Biden again, and voting third party. He views both as big pharma shills for both promoting the vaccine and while he hates Biden's Ukraine policy, he is also skeptical of Trump's lofty promise to resolve the conflict in a day. Upon Trump's classified document indictment, he now views Trump as very unstable and dangerous. Due to that and him agreeing more with Biden on most issues, he now plans on voting Biden again in the general despite his reservations. But until that point, he is all the way with RFK Jr.
By the way, if I change this person from a moderate Democrat to a progressive Demofrat (but with the same eccentric anti-vax/lockdown and anti-Ukraine funding views), then this can reasonably be a Sanders/Sanders/RFK voter.