Einstein kind of has credit for starting relativity AND quantum mechanics!
His 1905 work on the photoelectric effect revealed the quantisation of the electromagnetic field to the surprise of the scientific community, motivating the later work that explained this.
And he didn't stop there. See Einstein–Brillouin–Keller method.
It would be interesting. I am not 100% sure he would have been very comfortable with it. He was very much an engineer, not a physicist.
EDIT: a little research confirms my guess. His views on both QM and relativity are those of someone whose ego exceeds his understanding. He wrongly called relativity pseudoscientific, and hated QM (in a far less developed way than Einstein tried to show it was not the true theory). His other eccentric views included denying the existence of the electron (and subatomic particles in general) - he felt atoms were single entities without parts.
The scientific facts show how badly wrong he was. For example, the quantum mechanical model of the hydrogen atom finds precise solutions that have precise energy levels, and these energy levels are extremely precisely verified via emission spectra, down to very subtle features. Quantum field theory (the more precise theory that is built on quantum mechanics to incorporate relativity and the way in which virtual particles make any system an infinite particle system) takes this further to achieve the most precisely verified results in science.
Likewise relativity is a very precisely tested theory, with GPS satellites relying on special and general relativistic corrections to clocks that are good enough to get locations to within a meter, and general relativistic time dilation was verified over a vertical height of just 1 mm recently (clocks run slower when deeper in a gravitational field).
I did a little research on Tesla too.
Interesting how he rejected relativity and quantum mechanics.
In contrast to Einstein who got relativity started but then rejected quantum mechanics.
In contrast to Planck who accepted relativity and reluctantly accepted Heisenberg's new quantum mechanics - witnessing the 'funeral' of the determinism Planck preferred while Planck was in fact the original pioneer of quantum mechanics in the first place. It seems.