Design, theoretical modeling, and experimental characterization of a widely tunable Ti:Sapphire laser with nanosecond pulses and high pulse peak power is presented. The laser provides a continuous tuning range of from 675 nm to 1025 nm with no exchange of optics required. At a pulse rate of one kilohertz it delivers pulse energies of up to 2.5 mJ, pulse durations of around 20 ns, a spectral bandwidth of 10GHz and an almost diffraction-limited beam quality of M2<1.2 with a smooth characteristic of these parameters over the full wavelength range. This clearly exceeds the performance data published so far with our previous designs. Effects, which tent to provoke spectral gaps in the past, are totally understood and definitely suppressed by a modified resonator design. The presentation contains a detailed description and discussion of performance determining design aspects, i.e. pump scheme and pump beam shaping, resonator design and the comparison of different tuning elements. As a main prerequisite of an appropriate resonator design thermal lensing in Ti:Sapphire crystals is discussed on the basis of experimental and theoretical results. This includes the wavelength dependency of the focal length, the astigmatism in end-pumped Ti:Sapphire crystals with Brewster-cut end faces, the influence of the pump-light distribution and different cooling schemes.