Kyle Reese (Terminator): The machines send the Terminator back in time to kill Sarah Connor before she can have John. In response, the rebels send Kyle back to protect Sarah and as a result gets Sarah pregnant with John.

Babylon 4 (Babylon 5): Babylon 4 is thought destroyed but actually sent into the past and shows up due to a damaged time device. The Babylon 5 crew have to go to Babylon 4 to prevent it from being actually destroyed, they go because they saw a recording of it happening, so that  a present day Sinclair can go back in time to become Valen who when he does is eventually reborn as Sinclair which will help during the Earth/Minbari war when Delenn captures him and realizes Minibari are being reborn as humans.

Duke (Haven): Is sent back in time and winds up saving his grandfather which causes present day Haven to get even worse. He then tells his grandfather who is going to kill him and his grandfather then runs off to confront that person who winds up killing him. 



Timmy Turner (Fairly Oddparents): Timmy and Cosmo go back in time where they are responsible for not only making Crocker go batshit crazy about his obsession with fairies but also caused him to break up with Timmy's mom.

Nathan (Haven): Nathan is also sent back in time due to a letter that Duke wrote in the past where he meets a Sarah, a past incarnation of Audrey. They have a fling and as a result The Colorado Kid is born. Later Nathan goes back to the 80s to get information about Lucy (another incarnation of Audrey) and has to tell his adopted dad about what is going on...which is why he seemed to know so much in the present and was cagey about it. Nathan then has to watch with Lucy as the Colorado kid is killed.

Characters who went back in time to fix what went wrong only to find that the changes they made were meant to happen.