Little is known about Owain as a man. He was descended from the princely houses of Powys and Deheubarth, but his landed estate is reckoned by R R Davies to be worth £70 a year at most, which in England would have had him rated as an important member of the gentry, qualifying for knighthood, but nothing more. To put it in perspective, remember that Bolingbroke drew an income of around £1500 from the lordship of Brecon alone.
Owain was around 40 in 1400, which was well beyond youth in the 14th century - given that the average age of the population was nearer 20. He appears to have served the Arundel family in various roles, and he fought in Richard II's Scottish campaign of 1385. In terms of relationships he was connected to other Welsh gentry families, to people who might be called Anglo-Welsh, like his wife's people, the Hamners, and to English gentry such as his brother-in-law, Robert Puleston.
The spark for his rising appears to have been a quarrel with his neighbour, Lord Grey de Ruthin, who lived just over the hill from Owain. Some say it was a dispute over land, others that Grey held back a summons from Henry IV for Owain to join the king's invasion of Scotland. My impression of Grey is that he was an aggressive bully, and not particularly bright, but unfortunately (from Owain's point of view) he was also a close associate of the King. (I'm reluctant to say 'friend' as I think even Bolingbroke had better taste.)
Either way between 18th and 23rd September 1400, Owain's supporters attacked Ruthin, Denbigh, Flint, Holt and Oswestry. Henry's response was rapid (he had an army available, having just attacked Scotland) and after eight of those involved in the attack on Ruthin were executed the government felt strong enough to start issuing pardons to those involved and during October to disband most of the forces assembled to deal with the revolt.
Owain and a few supporters made off for the hills, neither pardoned nor reconciled. It must have seemed to Henry IV that this was just a minor local difficulty that had been sorted. His next parliament (otherwise busy with attainting Richard II's supporters) re-enacted penal statutes against the Welsh and added a few bells and whistles for good measure, just to show who was boss. To some extent at least this was prompted by the English minority communities in Wales, who had just had a very nasty scare. But it was scarcely an enlightened piece of statecraft, and it probably served as a wonderful recruitment sergeant for Owain. He was to be back.