Short answers, pulled from the story.
The first OVA to be billed as such was Dallos, released by Bandai in 1983. This release marked a shift in how animation reached audiences by existing solely on home video rather than television or theatrical schedules.
The earliest known attempt to release an OVA was The Green Cat in 1983. This series cannot count as the first OVA because there is currently no evidence that the VHS tape became available immediately and the series remained incomplete.
The consumer base of OVAs constituted mainly of males, with Bandai Visual reporting in 2004 that about 50% of customers were 25 to 40-year-old men. Nikkei Business Publications also stated that mainly 25 to 40-year-old adults bought anime DVDs.
The OVA market lost its status as a haven for adult content in the 1990s because the rising popularity of cable and satellite TV networks allowed public broadcasts of many new titles. These networks typically had less strict censorship, so many violent and risque series became regular TV series instead of OVAs.
Starting in 2008, the term OAD or original animation DVD began to refer to DVD releases published bundled with their source-material manga. This change reflected a broader shift in how audiences consumed media, moving away from the standalone rental model to integrated distribution.