Who were those two old guys?

Why would he (Brad Bird) honour these two old men by featuring them in The Iron Giant and The Incredibles?

Brad Bird was mentored by Milt Kahl and Eric Larson at a young age and became familiar with Frank Thomas and Ollie Johnston through them as there was a group of famous animators called the "Nine Old Men". He started visiting and heckling Frank and Ollie while getting to work closly with them in later years. When Frank and Ollie retired from production on a Friday, Bird became next animator sitting in the very same desk as Ollie sat his entire career the following Monday. This left Bird was in absolute awe, even saving Ollie's old pencil shavings and putting them in a jar calling them his lucky shavings! lol
Frank and Ollie were Bird favorite of the 'Nine', and just idolized them by putting them in as characters in two of his animations with the help of Mike Venturini, leaving them both surprised and delighted.





Frank Thomas was also the directing animator in The Lady and the Tramp and was the creator of the pencil test of Lady and the Tramp spaghetti scene.
As for Ollie Johnston, he was the main directing animator for Lady and did most of her work, with the exception of the spaghetti scene (Frank).