Gaston Breitling (about 1884–1927) was the only son of Léon Breitling, who had founded his watch workshop in Saint-Imier in 1884 and moved it to La Chaux-de-Fonds, where in 1899 he named it L. Breitling, Montbrillant Watch Manufactory after the street on which it stood. Its early speciality was chronographs and counters, among them the Vitesse pocket chronograph, which measured speeds from 15 to 250 kilometres or miles an hour and, according to Breitling, was used by the Swiss police to issue the first speeding tickets.
When Léon died in 1914, aged 54, Gaston took over the company. In 1915, as the First World War began, he completed his father's work with the first wrist chronograph with an independent push-piece at two o'clock, used to start, stop and reset the chronograph; English Wikipedia credits him with the first wristwatch chronograph, with a central seconds hand and a 30-minute counter. The design was quickly put into industrial production, and the rest of the industry followed. After the economic turmoil of the war, the brand found success again in the 1920s. In 1923 he filed patent 105532, a system in which the chronograph could be stopped with the two o'clock pusher and reset independently through the crown, allowing successive times to be added without returning to zero; Breitling describes it as laying the groundwork for its later two-pusher chronograph.
Gaston Breitling died on 30 July 1927. His son Willy was only 14, and his widow Berthe kept the company running until, in 1932, Willy, then 19, persuaded her he was ready to lead it.
Correction: Casadi's earlier record had him leading the company until 1935. Wikipedia and Breitling show that he died in 1927 and that his widow ran it until Willy Breitling took over in 1932. His birth year is inferred from his age at death.