Obadiah Bull is said to have been an Irish lawyer who lived and practised in London during the reign of Henry VII (1485–1509).
His last name is supposed to have been the origin of the term "That's a Bull", for nonsense[1] or a blunder made by an Irishman.
1708) that ‘it became a Proverb from the repeated Blunders of one Obadiah Bull, a Lawyer of London, who liv'd in the Reign of K. Henry the Seventh’.)"
Equally, the Oxford Dictionary of National Biography contains no Obadiah Bull.
O[ld] F[rench] boul, boule, bole fraud, deceit, trickery; mod[ern] Icel[andic] bull ‘nonsense’; also M[iddle] E[nglish] bull BUL ‘falsehood’, and BULL v.3, to befool, mock, cheat.")