Kenneth (or Ciniod) MacAlpin was born around 810 CE, the son of Alpin MacEochaid, first King of the Scots (although the region of Dalriada remained under Pictish rule at that time, and Alpin's power base lay in Galloway).
Kenneth's mother was either the daughter of a king of Argyllshire or a Pictish princess: in either case he through her obtained a right to ascend the throne of Caledonia).
Alpin and his son both resented the Pictish influence over the broader Scots territory. Sometime between 834 and 840CE Alpin died in battle against the Picts but all this achieved for the "painted folk" was an opportunity to face (and be soundly defeated by) the Scots Vikings, losing their king and his brother.
Kenneth took the Dalriadic throne in about 841AD, taking it into independence, and he pressed his claim to the Caledonian throne, but this remained for the moment in Pictish hands, under Drust, although the Vikings continued to occupy swathes of land. Kenneth invited the seven Earls (or mormaers) of Caledonia to a feast to discuss tactics, but in the morning all seven, and Drust, were dead, and Kenneth united the thrones of Scots and Picts into Alba and took the throne as Kenneth I. He moved the capital from Dundald to Scone, and moved the Stone of Destiny, upon which kings were crowned, to Scone as well.
He ruled until his death in 859 and was succeeded by his brother, Donald I. During his reign he held off the Vikings from further encroachment and also crossed into Anglian Bernicia to secure his southern borders.
He married, to a cousin's daughter, as a means of maintaining his standing. She bore him two sons, Constantine and Aedh, each of whom were to ascend the Scots throne for short periods, and from whom the House of Alpin was to grow. Some histories also say that Kenneth I made dynastic marriages with his daughters, marrying one to Olaf, the king of Dublin; a second to a High King of Ireland, and a third to Rhun, prince of Strathclyde.