 He transitioned from child TV star to adult character actor, deliberately taking roles in which he could vary his appearance and attitude to the extent that in the 1980s Robert Osborne, then columnist for "The Hollywood Reporter" and later TCM host, named him “a master of disguises.”

Live theatre is Burr’s favorite performing medium.His 45 drama, comedy and musical theatre performances include Gower Champion’s original Broadway production of "Mack & Mabel" (1974-75) with Robert Preston and Bernadette Peters; two productions of "George M" (1969), the first National Company with Joel Grey and on his own in a 1983 Las Vegas production; "Death of a Salesman" (1999) at the Olney Theatre Center; the Ford’s Theatre (Washington DC) production of "The Grapes of Wrath"(2005); a second revival of "No, No Nanette"; "The Boys From Syracuse" (Goodman Theatre, Chicago ); the premiere of "Over The Hill”, a comedy he also wrote and directed; as the fascist Capitano Aldo Finzi in "Tamara", Los Angeles’ longest running play (nine years); and the year-long Los Angeles production of "42nd Street" (Shubert Theatre, Los Angeles).In Actors' Equity professional summer stock on both coasts, Lonnie co-starred as Spats Palazzo in "Sugar" with the late Arte Johnson, Marcellus in "The Music Man" with Peter Marshall, with Ginger Rogers in "Coco", and with Elke Sommer in "Irma La Douce".