I have done extensive research, but in the DC universe, I have found nothing on time wraiths. When I watched the episode, I saw the time wraith was wearing a hood much like the one Barry Allen wears. Any ideas on what this thing is, and why it looks like a zombie ghost Flash?
From what I have read the Time Wraith is unique to the television show. I personally think that they are "ghosts" that are created if the timeline changes. Perhaps because Barry is the one who changed the timeline, that is why it bears his resemblance? Here is a link to an article that sums up what we know about the Time Wraiths:
While not a perfect parallel, the Wraiths are closely related to Black Flash, a character from the comics that is basically Death for speedsters.
The Time Wraiths seem to be Speed Force connected wraiths that are attracted to and angered by speedsters altering the timeline. We don't know exactly how they work but the Season 2 finale shows us:
The time wraith is like a time-police being that makes sure that you don't change too many things in the time stream. For example, when Flash went back in time to ask Wells a question, a time wraith followed him because Flash wasn't being careful about not changing the time stream. (He was immensely lucky that he didn't find everything different when he went back).
I'm not so sure in the comics. The other answers probably get that better.
The wraith is Barry Allen, or his speed essence from inside the speed force, corrupted after the death of Iris with only the will to prevent or punish future corruption of the time lines by other speedsters. If he manages to prevent her death, the time wraith, at least in his image, will cease to exist.
Since speed force is created by Barry Allen I think it's Barry who has turned into a time wraith , zoom didn't turn to a complete time wraith or he may never turn into a time wraith and he might be a servent for the rest of his life , the reason why I think it's Barry Allen is cause , speed force was created by him , and when it caught Barry Allen he was about become mummified just like the wraith unlike zoom ,
I am pretty sure dat the first time wraith was Barry Allen the creator of speed force itself , he was turned into a time wraith obviously cause of time travel , and while returning back got stuck in some other timeline , so he was there to prevent the same mistake done by younger Barry when he was traveling back in time , or it may be like if he stopped the younger from time travelling he might get his normal life back .
And to be clear only one time wraith came after Barry when he travelled back to get the speed force formula
But in zooms situation it was 2 time wraiths may be because he didn't time travel but he created 2 time remanents and killed them .
But when Barry created a time remanent the remanent sacrificed himself , I think it had become time wraith but got a chance to become human again since Barry created flashpoint , this is the reason why no time wraith was after Barry when he created flashpoint .
So conclusion , time wraiths are actually the respective speedsters , i.e., every speedsters has a time wraith which is his counterpart living inside the speed force , the time wraith is basically the future self of a speedster .
And for those of you who is asking why time wraith never attacked eobard thawne is because he uses the negative speed force which has laws of it's own , and this is the reason why reverse flashpoint is not created when he changes something in the past , even in the comics reverse flash himself states that only flash can turn back time , cause of the negative speed force eobard can create speed mirage , steal memories , and erase anyone out of existence .