From A Wiki of Ice and Fire
|Alias||the Laughing Storm|
|Title|| Ser |
Lord of Storm's End
Lord Paramount of the Stormlands
Storm King (briefly)
|Book(s)|| The World of Ice and Fire (mentioned)|
The Hedge Knight (appears)
Ser Lyonel Baratheon, known as the Laughing Storm, was a knight of House Baratheon during the reign of Daeron II Targaryen. He eventually became Lord of Storm's End. He had a son named Ormund Baratheon and at least one daughter. 
- See also: Images of Lyonel Baratheon
The Tourney at Ashford Meadow
Ser Lyonel participated in the Ashford Tourney. In the first tilt he challenged Ser Robert Ashford. After breaking nine lances they both lost their saddles on their tenth course, only to rise together to fight on, sword against mace. Finally a battered Robert Ashford admitted defeat, Ser Lyonel become a champion in his place.
He fought multiple matches, against lesser foes, he would often break into booming laughter the moment they touched his shield, and laugh all the time he was mounting and charging and knocking them from their stirrups. If his challengers wore any sort of crest on their helm, Ser Lyonel would strike it off and fling it into the crowd. He joined Ser Duncan the Tall in the Trial of Seven, knighting Raymun Fossoway shortly before it started.
Lord of Storm's End
During the reign of KIng Aegon V, Lyonel was Lord of Storm's End and a leal supporter of King Aegon's. So much so that King Aegon was pleased to arrange a betrothal of his eldest son and heir Prince Duncan Targaryen to Lord Lyonel's daughter.
However Prince Duncan later broke that betrothal when he fell in love and married a common born girl known as Jenny of Oldstones. This enraged Lord Lyonel who felt the honor of his House was insulted, he renounced his fealty to the Iron Throne and declared himself Storm King, a short rebellion followed that ended in a trial by combat between Lord Lyonel and Ser Duncan the Tall. Lord Lyonel was defeated and yielded to Ser Duncan. King Aegon pardoned him and to make peace with House Baratheon arranged a new betrothal of his daughter Princess Rhaelle Targaryen to Lord Lyonel's heir Ormund Baratheon. King Aegon sent Rhaelle to Storm's End as Lord Lyonel's cupbearer and companion to his lady wife to make sure this wedding took place.