Robert the Fearless tried to take over the Duchy of Normandy when his father, Richard II, died in 1026. Unfortunately, it went to his older brother, Richard III. Fortunately, Richard was the forgiving type, so he forgave the rebellion and then promptly died so that Robert got what he wanted anyway. Richard had it for 49 weeks. Robert got to hold the position for eight years.
Robert was now in charge, but his rebellion had lasting effects. The two brothers' factions still squabbled over whether Robert was considered a legitimate ruler. Robert's uncle, Archbishop Robert of Rouen and Count of Evreux, had supported Richard during the rebellion. Duke Robert decided to assemble an army against his uncle, forcing him to leave Normandy. He also attacked his cousin, the Bishop of Bayeux Hugo III d'Ivry, banishing him from Normandy. Robert also fell afoul of the Church further when he seized some church properties belonging to Fécamp Abbey, which was long connected to his family.
Apparently not being satisfied unless he was causing or involved in conflict, he promised military support to Count Baldwin IV of Flanders. This had a more noble reason: Robert's sister Eleanor was married to Baldwin IV. This Baldwin was driven from Flanders by his son, Baldwin V. Robert I's involvement made King Robert II of France persuade Baldwin V to make peace with his father in 1030.
When Robert II of France died in 1031, his (third) wife, Queen Constance, wanted her son Robert of Burgundy to succeed to the throne. King Robert had intended his elder son Henry to succeed him. Robert of Normandy got involved by sheltering Henry (unironically favoring the older brother and designated heir, as opposed to his own case). When Henry assumed the throne of France as Henry I, he rewarded Robert with the Vexin, an area between Rouen and Paris. (Incidentally, Robert's great-great-grandfather Rollo made several attempts to conquer that territory.)
Beyond the continent, he had interactions with England that are worth talking about...next time.
