The first leader of the patarini was Landolfo Cotta. He was also Sub-Deacon of the Archdiocese of Milan, and one of four candidates put forward by the Milanese clergy in 1045 to succeed Ariberto as Archbishop of Milan. The others, also patarini, were the previously-mentioned Arialdo of Carimate, Atto, and Anselmo of Baggia, who would later go on to become Pope Alexander II.
Although it was customary for the Holy Roman Emperor to accommodate the wishes of the local churchmen in naming the archbishop, Henry III chose instead to install one Guido of Valete, a simonist—i.e., a corrupt buyer and seller of church offices and indulgences.
Well aware of all the difficulties his father had experienced with Ariberto, Henry may have been wary of any candidate with too strong a base of local support. Then again, he may simply not have regarded Guido’s corruption as anything particularly noteworthy.
Landolfo Cotta and Arialdo responded to this reaffirmation of a cynical status quo by leading popular protests, in which the citizenry refused to accept the sacraments from corrupted priests.
Within a few years, the papacy also began to swing in the direction of reform. After the debacle of Benedict IX, Pope Leo IX attacked simony and concubinage among priests in 1050, and was backed in his reformist spirit by his successors.
Archbishop Guido, however, was not inclined to modify his practices on account of the mere installation of a new pope, and certainly not because of accusations made against him by the likes of Landolfo and Arialdo. In 1057, he took the simpler step of excommunicating Arialdo (and perhaps also Landolfo). Pope Stephen IX immediately overturned the excommunication(s), though, and urged the reformers to continue their work.
Later in 1057, Landolfo Cotta set out for Rome to present the pataria’s ongoing case against Guido to Pope Stephen. Along the way, he was ambushed in Piacenza by assassins sent by Guido. He managed to survive the attack, but just barely.
Landolfo went on to survive another assassination attempt in 1058, on the Monday of Passover, when he was stabbed while praying in church. He never fully recovered from this later attack, however, and eventually died of pulmonary complications in 1061.