Bohemond I of Antioch might well fit your requirements there. He was the eldest son of Robert Guiscard, Count of Apulia and Calabria, but one of his younger brothers managed to secure the succession and he was left with relatively modest holdings despite contesting things militarily for some years.

He joined the first crusade with a far from gigantic force but as a renown war leader, a veteran of fighting the Byzantine Empire (and his brother). He was an extremely capable commander and took the lead in the siege of Antioch before personally taking control of the city.

Once he had the city? He basically stopped taking further part in the crusades and focused upon his personal ambitions with mixed success.