We report measurements of quasiparticle relaxation dynamics in the high-temperature superconductor (Ba,K)Fe2As2 in optimally doped, underdoped and undoped regimes. In the underdoped sample, spin-density wave (SDW) order forms at ∼85 K, followed by superconductivity at ∼ 28 K. We find the emergence of a normal-state order that suppresses SDW at a temperature T * ∼ 60 K and argue that this normal-state order is a precursor to superconductivity.The recently discovered FeAs-based pnictides [1][2][3][4][5] constitute the only class of superconductors (SCs), besides the cuprates, with superconducting transition temperatures (T c ) exceeding 50 K. The pnictides have a layered structure like the cuprates, with FeAs planes instead of CuO 2 planes. Like many other SCs on the border of magnetism, such as the organics [6], heavy-fermions [7], and cuprate high-temperature superconductors (HTSCs) [8][9][10], the pnictides exhibit a rich phase diagram, with antiferromagnetism (or spin density wave, SDW) at low dopings [11] and SC at intermediate dopings. Figure 1(a) shows the phase diagram of a particular family of pnictides -(Ba,K)Fe 2 As 2 (BKFA) [12], which is the subject of study in this Letter. These phases in BKFA are mesoscopically separated in the underdoped compound, with SDW and SC/normal state regions [13]. Moreover, inelastic neutron scattering in an optimally-doped BKFA revealed the presence of a 14 meV magnetic resonance mode in the SC phase, localized in both energy and wavevector [14]. A large Fe-isotope effect was seen in BKFA, suggesting the role played by magnetic fluctuations in superconductivity [15]. In all these classes of SCs, how these phases interact with one another, and the role of magnetism, are open questions that might help understand superconductivity in these compounds.In the cuprate HTSCs, femtosecond pump-probe spectroscopy has shown to be a useful tool to discern coexisting/competing phases, such as the pseudogap phase in YBa 2 Cu 2 O 7−x (Y-123) [16], and the suppression of superconductivity by antiferromagnetism in the tri-layered Tl 2 Ba 2 Ca 2 Cu 3 O y [17]. In this Letter, we use the pumpprobe technique to study the BKFA SCs in the undoped, underdoped and optimally-doped regimes. In the underdoped sample, we observed the existence of three energy scales -SDW (at Néel temperature T N ∼ 85 K), superconductivity (at T c ∼ 28 K) and a normal-state phase (at T * ∼ 60 K). We observed the smooth evolution of this normal-state phase into the SC phase, and the suppression of SDW by this normal-state phase. We attribute this normal-state phase to the emergence of precursor superconductivity. We incorporated the existing ideas of phase separation and magnetic resonance mode, and introduced new ideas of spin susceptibility renormalization, emergence of precursor order, and the competition between SDW and superconductivity.Single-crystalline BKFA samples with sizes up to 10 mm x 5 mm x 0.5 mm were grown by high-temperature solution method [18]. The grown crystals were cleaved to reveal a fresh surfa...