Source:

“The obelus is believed to have been invented by the Homeric scholar Zenodotus, as one of a system of editorial symbols. They marked questionable or corrupt words or passages in manuscripts of the Homeric epics.”

Source:

“The obelos symbol (see obelus) gets its name from the spit, or sharp end of a lance in ancient Greek. An obelos was placed by editors on the margins of manuscripts, especially in Homer, to indicate lines that may not have been written by Homer. The system was developed by Aristarchus and notably used later by Origen in his Hexapla. Origen marked spurious words with an opening obelos and a closing metobelos (“end of obelus”).

Re: Origen, also see Hexapla:

…because of discrepancies found in [other] manuscripts had given occasion for doubt, we have evaluated on the basis of these other editions, and marked with an obelus those places that were missing in the Hebrew text […] while others have added the asterisk sign where it was apparent that the lessons were not found in the Septuagint…