"Upon an evil winter's heart, the heavy hand of regret infrequently alights. The malevolent path is one trod without the cumbersome shackles of sentimental introspec--" — An excerpt from Paragraph 4 of Inside an Evil Mind: The Dr. Wexler Story (As quoted by Perry the Platypus using a CD player[source]
Dr. Wexler's voice, as heard on the audiobook Agent P plays at Evil-Con, is similar to that of Professor Calamitous from The Adventures of Jimmy Neutron. This makes it very likely that Tim Curry is the actor for this character.
Since Dr. Wexler appears to be a British character, it's possible that he was born on the 1st of August instead of the 8th of January; this is due to the little endian form of dating, which is employed in the UK.
Doofenshmirtz mentioned him making a ransom note so this may hint he has kidnapped someone in the past.