LAST EDITED ON 01-13-09 AT 09:39 PM (EST)

A little more:

You really should see all of Season 2.

If you've seen Season 1, you know Tony. In Season 2, he becomes head of CTU after George dies and supports Jack and David Palmer against Ryan Chappelle and the VP, leading to his temporary arrest along with Michelle, an analyst who becomes his girlfriend. In Season 3, Tony and Michelle are married, Michelle gets kidnapped and Tony aids the terrorists to save her, leading to his arrest and imprisonment. In Season 4, Jack gets him back in action at CTU, and he and Michelle, along with ex-President Palmer and Chloe, become the only people who know that Jack is not actually dead. But at the start of Season 5, Palmer and Michelle are killed and Tony is almost killed; he is then apparently killed by an ex-mentor of Jack's gone bad.

Kim Bauer is supposed to be back in a limited role. In Season 2, Kim plays Our Lady of Perpetual Peril. In Season 3, she joins CTU, working for her dad. Her best friend and co-worker is Chloe. Kim then leaves the show (supposedly to get married to Jack's former partner, who lost his arm in the last episode), but in Season 5, she returns for a cameo with a new boyfriend, a self-help guru type. He's not back, so I know nothing else.

Chloe was a key person in Season 3, but beginning with Season 4, she became Jack's key aide, the way Michelle was in Season 2. At the end of Season 5, we learned that she had an ex-husband Morris, a former CTU staffer, and during Season 6 we found that they had gotten back together and learned at the end that she was pregnant.

Bill Buchanan originally came on as an overseer of CTU who had had a relationship with Michelle while Tony was in prison in Season 4. When Michelle retires from CTU at the end of Season 4, Bill is placed in charge and was there through Season 6.

Here are the presidencies:
Season 1: during the campaign, before David Palmer wins.
Season 2: during Palmer's first term
Season 3: at the end of Palmer's first term; he decides not to run for re-election
Season 4: during the term of Palmer's successor, President John Keeler. Keller is replaced by VP Charles Logan.
Season 5: during Logan's remaining term. Appointed VP Hal Gardner has to finish up Logan's term (if you haven't seen this season, I won't tell you why).
Season 6: shortly after the inauguration of new President Wayne Palmer, Gardner's successor. He is replaced by VP Noah Daniels.
Season 7: shortly after the inauguration of new President Allison Taylor, Daniels' successor.

So we've had the following one-term administrations:
0 (Season 1)
1: David Palmer (Seasons 2 & 3)
2: John Keeler/Charles Logan/Hal Gardner (Seasons 4 & 5)
3: Wayne Palmer/Noah Daniels (Season 6)
4: Allison Taylor (Season 7)