The Trickster's Brigade

The Trickster's Brigade was a group of creatures intent on changing the timeline in subtle ways for reasons unknown. They would attach Time Beetles to unsuspecting victims (it's actually suggested that Time Beetles are actually part of the Brigade itself, rather than a tool, but this is not made completely clear), and then change an influential event in that persons past in order to profit from the changes in the timeline this created. Usually such changes would have little effect on history, as time compensated around it, but in some circumstances, with victims who had a particularly great influence on the universe, the change would create an entire parallel world around that person.

while the dialogue might be interpreted to imply that Time beetles and the Trickster's Brigade are one and the same thing, in Doctor Who Confidential Russell T Davies suggests they are not, and furthermore Captain Jack's Monster Files suggests the Brigade might use other creatures.

One Time Beetle attached to Donna Noble on the planet Shan Shen, with the help of a Fortune Teller tricking donna into becoming succeptible to it's influence

The change it caused was to stop Donna from working at H.C. Clements. This in turn stopped her from meeting the Doctor, and so he died in the Empress of the Racnoss's lair under the Thames Barrier. However, with the help of Rose Tyler from Pete's World, this change in history was reversed and the member of the Trickster's Brigade died. (DW: Turn Left)

It was suggested that the Trickster's Brigade was affiliated with the Trickster in Captain Jack's Monster Files. The Trickster had previously threatened to erase the Doctor after an earlier attempt to do the same to Sarah Jane.